1997 gmc jimmy hard 2nd gear shift

I recently had my trans go out took it to a transmission shop. they said they had to rebuild transmission. got truck back and had a hard shift to 2nd gear. took it back to shop they said it needed a external trans cooler for hot fluid. got it back same issue with 2nd gear took it back again and they said it could be the valve body but called same day and said it was the speed positioning sensor. any suggestions on why it shifts hard after rebuilt trans.:banghead:

The valvebody in these transmissions started giving trouble several years ago and some were even changed out under warranty...mine was changed out prior to my purchase as a good faith measure.
Here's some info.
http://www.automotiveforums.com/vbulletin/showthread.php?t=640952&highlight=transmission+valve+body