GM used two six-speed automatic transmissions in the 2007–2013 GMT900 platform: the 6L80 and the 6L90. Here’s how to tell them apart and what it means for you.
The Short Answer:
- 6L80 – Used in 1500 series trucks and SUVs with the 5.3L and 6.0L
- 6L90 – Used in heavy duty (2500HD/3500HD) trucks with the 6.0L, and some Escalade/Yukon Denali applications with the 6.2L
How to Tell Them Apart:
Check your door sticker (Service Parts Identification sticker) or the RPO code. Look for “M70” (6L80) or “MYC” (6L90).
Specifications Comparison:
| Spec | 6L80 | 6L90 |
|---|---|---|
| Max Torque Capacity | ~450 lb-ft | ~520 lb-ft |
| Gear Ratios | Same 6-speed layout | Same 6-speed layout |
| Physical Size | Smaller | Larger, heavier |
| Fluid Capacity | ~11 quarts | ~13 quarts |
| Max GVWR Application | 1/2 ton | 3/4 ton & up |
Common Issues on Both:
Both transmissions share similar design features and similar failure modes:
- TCC (torque converter clutch) shudder
- Harsh shifts when fluid is old or degraded
- 4th gear hesitation
- Solenoid failures at high mileage
Fluid Service:
Both the 6L80 and 6L90 use Dexron VI ATF. GM recommends fluid service every 45,000 miles under normal conditions, or every 30,000 under towing/severe use. ACDelco Dexron VI ATF is the OEM-specified fluid.
Pan Filter Capacity:
A drop-pan filter service typically removes and replaces about 5–6 quarts. For a full fluid exchange, use a transmission flush machine.
Upgrade Potential:
Both transmissions respond well to a deep aluminum pan upgrade for better fluid capacity and cooling during towing.
Which trans did your GMT900 come with? Drop your RPO code and application below!