Keep routes moving and crews working. Our Monster 4L80, 4L85, and 6L90 builds for NPR/NPR HD add durability, cooler temps, and confident lock-up for real workdays.
From legacy fleets to later gas NPR HD trucks, we match your model years and use-case. Choose the correct unit below—or call us with your VIN and we’ll confirm fitment.
Our 4L80 commercial builds focus on heat management and clutch durability for frequent starts, stops, and in-town routes.
Added clutch capacity and upgraded hydraulics to handle heavier bodies and stop-go cycles common in service and box-truck use.
Modern six-speed with targeted upgrades for lock-up control, thermal stability, and shift quality under continuous urban duty cycles.
| Model Years | Model | Use Case | Transmission |
|---|---|---|---|
| 1993 – 1998 | NPR | Urban delivery, light box, service bodies | 4L80 |
| 1999 – 2007 | NPR / NPR HD | Heavier bodies, frequent stop-and-go | 4L85 |
| 2012 – 2019 | NPR / NPR HD (later gas) | Modern six-speed duty, mixed routes | 6L90 |
On changeover or upfit builds, share your VIN and body details—we’ll confirm the correct unit and converter spec.
Commercial duty means heat, weight, and stop-go cycles. We build for that reality.
Upgraded materials, precise line-rise, and converter options to keep temps in check.
Hydraulic and timing calibrations that stay consistent with payload on board.
We match stall and lock-up strategy to route profile and body weight.
Each unit completes a multi-point dyno test and QC cycle before shipping.
Streamlined logistics and straightforward core returns minimize downtime.
Talk to specialists who build 4L80/4L85/6L90 every day—get the right spec first time.
Common questions from fleet managers, upfitters, and independent shops.
We recommend staying with the correct era. Internal hardware and calibration differences can affect durability and drivability. Share your VIN and we’ll confirm the exact spec.
Yes. Clear adaptives and perform a relearn drive cycle. This allows the TCM to match pressure and timing to the fresh unit and converter.
Use the OEM-specified ATF for your transmission family (e.g., Dexron-compatible for 4L80/4L85 and the correct spec for 6L90). Follow shortened intervals for stop-go and high-heat routes.
No—ratings are set by the manufacturer. Our builds improve durability and shift quality so your truck performs more consistently within its rated capacity.
Ensure cooler paths are clear, consider an auxiliary cooler, keep converter lock-up healthy, and stick to proactive fluid service intervals.