The GM 6L80E / 6L90E 6-Speed Auto (LS3 / trucks / heavy duty) is a six-speed automatic.
First gear is 4.027:1 and 6th is 0.667:1. Divide one by the other and the overall spread is 6.04:1. That is a very wide spread. With six gears to share it out, the steps in the middle can still stay civil.
6th is an overdrive at 0.667:1: the output shaft turns faster than the input shaft. Two of the six gears are overdrives. No gear is exactly 1.00:1, so there is no direct drive.
The biggest step is 1st to 2nd, where the ratio drops 41%. The smallest is 5th to 6th at 22%. A drop that size lands the engine well down the rev range after the change, so it pays to know where the torque lives.
The final drive lives in a separate diff, so the speed table shows three common ratios: 3.42, 3.73 and 4.10. With a 3.73 final drive and 225/45R17 tyres, 6th at 6,000 rpm works out at 288 km/h (179 mph), and first runs out at 48 km/h (30 mph). That is how tall the gear is, not a top speed. Drag and power decide that. At 70 mph in 6th the engine turns about 2,340 rpm.
Ratios
| Gear | Ratio | Step |
|---|---|---|
| 1st | 4.027:1 | - |
| 2nd | 2.364:1 | 41.3% |
| 3rd | 1.532:1 | 35.2% |
| 4th | 1.152:1 | 24.8% |
| 5th | 0.852:1 | 26.0% |
| 6th | 0.667:1 | 21.7% |