Old Transmission for new one?

I have an 04 grand prix with a bad tranny and my friend has a 1992 buick regal with the same 3.8L engine. Im wondering if it is possible to use the older transmission from his car in my newer car. I was told the sensors would be the only difference.

No, they are not the same. The 92 has the 4L60 transaxle which still used a vacuum modulator to control part throttle shifts. Your 04 has the 4T65E version, which is completely electronic, so the 4L60 would not work properly in your car. Other issue would include VSS (Vehicle Speed Sensor) compatibility, axle length, final drive ratio, etc...

No, they are not the same. The 92 has the 4L60 transaxle which still used a vacuum modulator to control part throttle shifts. Your 04 has the 4T65E version, which is completely electronic, so the 4L60 would not work properly in your car. Other issue would include VSS (Vehicle Speed Sensor) compatibility, axle length, final drive ratio, etc...

Would a 2000 gtp tranny fit? Would anything before 2004 fit?

You didn't mention if your 04 GP is a GT or GTP model. The GT comes with the standard M15 version of the 4T65E transaxle, where the GTP comes with the MN7 heavy duty version which are not interchangeable. The 00 GTP tranny also uses the HD version, but is different than the 04-05 GTP trans. The HD version of these transaxles have a heavier differential, which requires a shorter passenger side axle, as well as a different final drive ratio (3.05/3.08 vs 3.29). Also, the 2nd design 03, and 04-05's use a different type of neutral safety switch vs the old models . So in short, you need to get a trans that matches your vehicle, most likely out of a similarly equipped 04-05 model (or a 2nd design 03), the older ones are not compatible.