The Peterbilt 579: Sibling Rivalry With the T680
The Peterbilt 579 shares its bones with the Kenworth T680 — same PACCAR MX-13 engine, same TX-12 transmission, same PACCAR dealer network. Both trucks roll off PACCAR assembly lines using shared platform architecture. So why does the 579 exist, and how does it differ from the T680 that sits in the next bay at the dealership?
The differences are in the details. Peterbilt has historically positioned itself as the more stylish, status-oriented brand within the PACCAR family. The 579's cab design is distinctly different from the T680 — a more sculpted hood, wider windshield rake, and a front end that projects a bolder road presence. Inside, the dashboard layout diverges significantly. Peterbilt uses a center-stack instrument panel design that groups gauges and controls differently than Kenworth's wraparound layout. Driver preference between the two is genuinely subjective.
Pricing falls between the Cascadia and the T680. A new 579 with comparable equipment to a T680 typically runs $2,000-$5,000 less — Peterbilt's concession that the T680 has slightly stronger brand demand in the owner-operator segment. That said, the 579 has its own loyal following, particularly among drivers who came up through company fleets that ran Peterbilt. For owner-operators comparing the two PACCAR siblings, the engine, drivetrain, and dealer support are identical — your decision comes down to cab ergonomics, styling preference, and resale demand in your local market.
The UltraLoft Sleeper: Peterbilt's Flagship Innovation
The 579 UltraLoft is Peterbilt's answer to drivers who want apartment-level livability on the road. The 80-inch UltraLoft sleeper stands 8 inches taller than the standard high-roof option, creating a genuine stand-up living space with over 7 feet of interior headroom. This is not a gimmick — for tall drivers or anyone who values being able to move around their sleeper without hunching, the UltraLoft is a game-changer.
The interior layout maximizes the additional space intelligently. A full-width lower bunk at 42 inches, a fold-up dinette table, expanded wardrobe closet, and a pantry-style storage cabinet give you more organized living space than any competitor except the Volvo VNL 860. The optional Platinum interior package adds premium upholstery, LED mood lighting with adjustable color temperature, a 24-inch flat-panel TV mount, and dual-zone climate control for the sleeper — independent from the cab HVAC.
The trade-off is weight and aerodynamics. The UltraLoft adds approximately 400-600 pounds over a standard 72-inch sleeper and creates a taller profile that increases wind resistance. Real-world fuel economy impact is 0.2-0.4 MPG compared to the same truck with a standard sleeper. At 120,000 annual miles, that is $1,400-$2,800 per year in additional fuel cost. If sleeper space is your priority, that fuel penalty is likely worth it. If fuel economy is paramount, the standard 72-inch sleeper gives you 90% of the livability at zero aerodynamic penalty. Use /tools/fuel-cost-calculator to quantify the difference for your mileage.
Driving Dynamics and Highway Performance
Behind the wheel, the 579 delivers the same PACCAR MX-13 power as the T680 — 380-510 horsepower, 1,450-1,850 lb-ft of torque, and a powerband that feels smooth and linear from idle to redline. The TX-12 automated manual shifts crisply and responds well to throttle input. Engine brake performance is excellent at up to 408 brake HP, which is critical for mountain driving and reduces foundation brake wear significantly.
Where the 579 feels slightly different from the T680 is in steering response and front-end compliance. Peterbilt uses a different front axle geometry that some drivers describe as slightly more responsive in lane changes and curves. The difference is subtle — most drivers would not identify it in a blind test — but it exists. The 579's cab-forward design also provides a marginally wider field of view compared to the T680, particularly at the lower windshield edge.
Road noise at 65 MPH is competitive with the T680 but slightly louder than the class-leading quiet of the Kenworth or Volvo VNL. The 579 uses a similar level of cab insulation but the dashboard design creates slightly different acoustic properties. On rough roads, the 579's ride quality is nearly identical to the T680 thanks to shared suspension architecture. The standard Peterbilt SmartAir rear suspension uses air springs that automatically adjust ride height and damping based on load weight — a feature that keeps the ride consistent whether you are bobtail or loaded to 80,000 GVW.
Maintenance Schedule, Costs, and Known Issues
Because the 579 shares the PACCAR MX-13 engine and TX-12 transmission with the T680, the maintenance profile is nearly identical. Oil changes every 50,000 miles ($350-$450 at a dealer), DPF service as needed (typically every 200,000-300,000 miles at $500-$800), and transmission fluid checks at each oil change interval. PACCAR's extended drain intervals are among the longest in the industry, which reduces both maintenance costs and shop time.
ATRI-benchmarked fleet data shows the 579's maintenance costs at $0.18-$0.21 per mile — identical to the T680 and competitive with the Cascadia's $0.17-$0.20. The shared PACCAR platform means any common issues affect both trucks equally. The MX-13 aftertreatment system (DPF, SCR, and DEF dosing) is the most frequent source of shop visits, though most issues are resolved with software updates or sensor replacements under $500.
The 579-specific issue to be aware of is the dashboard and instrument cluster. Several model years have experienced intermittent display glitches — the center screen freezing or displaying incorrect data. PACCAR has issued software updates that address most instances, but it remains a nuisance that T680 owners report less frequently. Also, the 579's cab entry steps have a slightly different design that some drivers find more slippery in wet conditions — aftermarket grip tape ($20-$30) is a common day-one modification. Track every maintenance event and benchmark against ATRI data at truckingresearch.org to spot cost trends early.
Resale Value and Market Demand
The Peterbilt 579 retains 40-46% of its MSRP at 350,000 miles — slightly below the T680 at 42-48% and the Cascadia at 45-50%. The resale gap is not because the 579 is a worse truck — it is because the Kenworth brand commands marginally stronger demand in the used owner-operator market. Peterbilt's strength historically has been in fleet sales, where the 579 is extremely popular. Fleet buyers prioritize spec consistency and dealer support over brand cachet.
Regional demand matters. In Texas, the Peterbilt brand is iconic (the company is headquartered in Denton, TX) and 579s sell faster and for higher prices than in other regions. In the Pacific Northwest and Midwest, Kenworth dominates the used market. On the East Coast, Freightliner leads. If you plan to buy in one region and sell in another, factor in these regional brand preferences — they can swing resale price by 5-8%.
For the best resale outcome, keep the truck in full DOT inspection-ready condition, maintain detailed service records through the PACCAR dealer network (dealer-documented maintenance commands a premium), and consider selling at 400,000-500,000 miles before any major powertrain work is needed. A clean 579 UltraLoft with full records and recent tires sells 20-30% faster than a comparable truck without documentation. See our full truck comparison at /guides/best-semi-trucks-owner-operators for where the 579 ranks in the broader market.
Final Verdict: Who Should Buy the Peterbilt 579
The 579 is the right truck for owner-operators who want PACCAR build quality and engine reliability at a slightly lower price point than the Kenworth T680. If you want the UltraLoft sleeper — the tallest and most livable sleeper cab in the class 8 market — the 579 is your only choice, since Kenworth does not offer an equivalent option. For drivers over 6 feet 2 inches tall, the UltraLoft's extra headroom alone can justify choosing the 579 over any competitor.
The 579 is also a strong choice for owner-operators based in Texas or the Southern market, where Peterbilt brand loyalty is strongest and resale values are highest. The PACCAR MX-13 engine, TX-12 transmission, and shared dealer network with Kenworth mean you are getting identical powertrain reliability and support regardless of which PACCAR badge sits on the hood.
Do not buy the 579 if you prioritize fuel economy above all else — the Freightliner Cascadia at /guides/freightliner-cascadia-review wins that battle by 0.3-0.5 MPG. Also think carefully about the UltraLoft's weight and aerodynamic penalty if you are running weight-sensitive freight where every pound matters. For most OTR owner-operators, the Peterbilt 579 with the standard 72-inch sleeper offers an outstanding balance of comfort, reliability, and value. The UltraLoft is the premium option for those who can absorb the fuel economy trade-off in exchange for unmatched sleeper livability.
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