[87Skier]

The 6L90 is a revised version of the 6L80. It is said to have been designed to replace the 4L80 (in form and function), and uses clutch-to-clutch shifting and does away with bands completely. The 80 and 90 share about half their parts. They have the same gear ratios:

1st - 4.027
2nd - 2.364
3rd - 1.532
4th - 1.152
5th - 0.852
6th - 0.667
R - 3.064

Production started around 2005, and are being pretty much replaced by the 8L90. Evidently, you can only get a 6L90 in a 1500 series new truck. All the rest have 8L90's. You can find them in Camaro's, Corvette's, vans, and trucks in both 4wd and 2wd versions mostly between 2006-2016.

These are not Allison transmissions.

They require a CAN bus to operate, so they came behind gen IV ls engine.

The 6L80 uses a 32 spline output that is the same spline as a 4L80.
The 6L90 received a 29 spline for 4wd applications and a 36 spline for 2wd applications.