I picked up a 1995 K1500 this weekend with a 5.7 tbi, 4L60E trans and a 7427 PCM

It has a problem with the trans/PCM interface. It will operate in 1-2 gear but will not shift any higher. If you pull the fuse it will shift to 3rd and stay there.

PO stated that these problems started after a break in and some work on replacing the whole dash assy and he thinks they pinched a wire.

Any diagnostic work I need to do right away?