Unfortunately this is not a rhetorical question. Overdrive did not want to work on my '01 this morning. I have heard this can be a problem with the early Gen. 6. It's got around 85K.
The '04 behind the barn was running perfectly when I parked it a couple years ago at 150K (body rotted out).
Anybody know if it is possible to swap the two trannies? I know they are not the same.

 

Both use the 4t65e transmission, but I am not sure if GM has any year specific changes. Perhaps someone else can chime in. Also, you may want to google this topic or consult with TripleEdgePerformance.

 

Ive heard that 00-02 are interchangeable and 03-05 are interchangeable. -But as said above, TEP would give you the info you need for sure.

 

The only year ranges you can work with is 2000-2002 for your 2001 application. All 2003+ 4T65E transmissions are electrically different and will not backwards retrofit without a lot of work and headache as well as custom tuning.

You will need to match the ID tag code for a direct replacement. There are two large letters on the ID tag on the back of your transmission case, this is what you need to match

 

Thanks for the info Chibi. I thought there was ' something'.
Good news (less bad news?) is that my mechanic just called, thinks it is NOT the transmission -- he believes the hesitation etc was caused by a plugged cat. converter. Does that sound reasonable?
Just curious, if it is/was the transmission, would it be possible/reasonable to pull/swap the engine and tranny together?
I'll start a different thread for the cat. converter.