What would happen?
I have a transport -91 whith the 3 speed automat and im thinking of a swap to the 4T60E instead, any problems or would it work whitout alot of work??
The engine is 3,1 l.

That is something I was fond of during the 60"s: anything could be swapped with anything - with a little work of course. But now, even if the hardware can be put in place, then you have an electronic control box that is both intelligent but totally unable to understand that you would now have a 4 speed gearbox. My best guess is that may be you might find the computer for a similar arrangement used on other GM cars - 3.1 with 4 speed - but I really think that overall, it would be a real headache: wire harnesses, etc...
I would just appreciate that someone can announce me that it is actually possible with ordinary means: I would like to learn of that.

Hi
I don't think that a changing to 4T60E is possible. Some friends in our forum www.pontiac-transsport.de changed the transaxle from a 3.8 1993 4T60E with a 4T60E from a 3.8 1994 and they had problems. The electrical connector is the same, but GM has changed the pin assignment, so nothing works. Also the 1994 4T60 has a temperature sensor, that is missing in 1993 and 1992

greetings
Bessi

the only swap that might be possible due to your vehicle not having the proper ecm for the shift controls would be more expensive than it's worth. You would need a complete donor vehicle that has a 4t60e and would have to swap the ECM, wiring harness, axle shafts, trans, etc.... making this swap impractical at best