Expert GMC Sierra 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.
1999 - 2006: 4L60-E on V6/small V8; 4L80-E on heavy-duty (Sierra 2500/3500). 2007 - 2014: 6L80 six-speed on Sierra 1500 5.3L/6.2L; 6L90 on Sierra 2500 gas. 2015 - 2019: 8L90 eight-speed on Sierra 1500 V8. 2020 - 2024: 10L80 ten-speed on Sierra 1500; 10L90 on 6.2L. Sierra 2500HD/3500: Allison 1000 on Duramax diesel (2001 - present).
Sierra transmission work is identical to Silverado - same transmissions, same parts, same procedures. 6L80 pump failures require a complete rebuild. 8L90 TCC shudder is addressed first with Dexron HP fluid exchange. Allison 1000 service is a specialized rebuild given its commercial-duty capacity - we stock Allison rebuild kits.
6L80/6L90 and 8L90 use Dexron VI or Dexron HP respectively. 10L80/10L90 use Dexron HP. 4L60-E uses Dexron VI. Allison 1000 uses Allison TES-295 fluid.
6L80 rebuild: 3 - 4 days. 8L90 TCC service: same day. Allison rebuild: 4 - 5 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.
Identical - same 6L80, 8L90, or 10L80, same parts, same repair procedures, same pricing. Sierra and Silverado are badge-engineered siblings with no drivetrain differences.
It's the 8L90 TCC shudder - common on 2015 - 2019 Sierra 1500. Not an emergency but it will progress. Start with a Dexron HP flush. If it persists, torque converter replacement.
3 - 4 business days. We stock 6L80 rebuild kits for same-week turnaround.
Likely - the Allison 1000 develops solenoid wear under sustained heavy-tow use. Get a diagnostic to confirm before assuming a rebuild is needed.
Yes - free towing within 15 miles of our shop on repairs over $500. Call (312) 626-8759.
Same-day appointments available. Honest estimates, no surprises. We've been doing this since 1987.
