Transmission History by Year - GMC Sierra 2500HD
2001 - 2010: Allison 1000 6-speed (Duramax diesel); 4L80E or 6L90 (gas) 2011 - 2019: Allison 1000 continued; 6L90 for gas 2020+: Allison 10L1000 (Duramax) or 10L90 (gas)
Expert GMC Sierra 2500HD transmission service in Chicago. Free computer diagnostic, 2-year / 24,000-mile warranty on rebuilds, all years.
We will contact you as soon as a service member is available by call, text, or email.
2001 - 2010: Allison 1000 6-speed (Duramax diesel); 4L80E or 6L90 (gas) 2011 - 2019: Allison 1000 continued; 6L90 for gas 2020+: Allison 10L1000 (Duramax) or 10L90 (gas)
Same approach as Silverado 2500HD. Allison TCC: converter and valve body inspection. Gas 6L90: SRV sleeve repair first. Allison 10L1000 issues: solenoid inspection, PCM update check.
Allison: TES-295 Dexron HP 6L90: Dexron VI
Verify exact spec on the dipstick label or owner's manual before fill. Recommended change interval: every 60,000 miles for normal driving, 30,000 miles under severe service (towing, stop-and-go, hot climates). Pan service typically takes 6 - 8 quarts; a full fluid exchange takes 10 - 14 quarts depending on cooler-line capacity.
6L90: 3 - 4 days. Allison: 4 - 6 days.
Fluid service and inspection complete the same day. Solenoid or sensor replacement: 1 day. Torque converter or seal repair: 2 - 3 days. Full rebuild with road test: 4 - 6 days. Time estimates assume parts in stock - call (312) 626-8759 to verify availability for your specific vehicle.
Every vehicle needs diagnosis before anyone can promise a repair path. These are the situations we help organize before you decide what to do next.
Tell us when it happens, whether reverse still works, and if warning lights are on. A scan and fluid check come before guessing at a rebuild.
Fluid condition, leak location, and driving distance matter. If the vehicle is slipping badly or overheating, towing may be the safer next step.
A failed solenoid, valve body, converter, or internal clutch problem can lead to very different repair paths. The goal is a clear diagnosis and written estimate.
Both are capable transmissions. The Allison has a stronger clutch pack design; the 6R140 is more calibration-sensitive. Both are rebuildable.
That's TCC slip in the Allison under load - a converter issue. Bring it in before you damage the valve body.
4 - 6 business days for a full rebuild.
Yes - diesel and gas Sierra 2500HD and 3500 are a regular part of our business.
Yes - we have a heavy-duty flatbed. Free within 15 miles with repair over $500.
Same-day appointments available. Honest estimates, no surprises. We've been doing this since 1987.
