Will a transmission from a 1995 Regal GS fit in a 1993 LeSabre? I mean a direct bolt-in with no modifications. They are both 4t60e's of course.

You might have a problem with the gear ratios some are 3.06 & some are 2.86.

So if the gears are the same its a bolt-in? And if they are not the same ratios what would be the problem? Speedometer off? Can a part be changed to fix that?

Actually it's worse than that. The 94-Up models have a different pinout on the electrical connector than the 91-93. This has been discussed on this board before. For more details on the wiring changes you would need to make, see the 4T60E ATSG manual page 10.

Here is a quote from that manual on page 11:

"CAUTION--CAUTION--CAUTION
The addition of the temperature sensor in the 1994
model 4T60-E transaxles required that the pin
functions be completely re-assigned........"

This will give you an idea of the different pin-outs on the connector: Oh, and don't forget, some have a 2.97 ratio also. :iceslolan
http://img96.imageshack.us/img96/8750/4t60ewiringqu6.gif