2007 Yukon. Lost 1st and reverse gears in transmission. Replacement options?

[Marky Dissod]

I have not done anything to it yet. Just looking for the part.
So I have the 6L80E. Interesting. Then why did it fail if it's more robust?

You say you have not yet done anything to it.
Does that include not changing the ATF? If so, how many miles has it gone without an ATF change?

 

[Geotrash]

I have not done anything to it yet. Just looking for the part.
So I have the 6L80E transmission. Interesting. Then why did it fail if it's more robust? I never towed with it.

The '07 has an early version of the 6L80 before it was in the field long enough for weaknesses in the design or manufacturing process to show up. In Nick's 6L80 thread, he details what those are. And many of them have little to do with how it's used. Its design is quite stout in terms of power handling capabilities, but there are problems like the TC, and one of the clutch drums that has weak welds, and check balls in the valve body that can show up as problems. Honestly though, 17 years out of a transmission ain't bad.