Transmission won't shift

Could've put undo strain/wear on the bands, clutches, gear sets, and who knows what shape tranny was in to begin with, given a 25 year old vehicle with a rebuilt motor. His driving technique almost certainly caused tranny to run hot, especially if he was maintaining normal or highway driving speeds in a lower gear. Newer cars/trucks will bump up to the next gear even if you've selected L or 1 or 2, when engine goes over a certain RPM precisely to prevent damage to engine/tranny. I don't think your 96 could do this, so he ran it in a low gear while cruising for extended periods of time it seems. You could test fluid pressure, or look for worn bands and/or clutches, as well as check for a burnt smell.

From what I was told he would shift it up when he decided the RPMs was high enough, as in a manual. I am not sure about highway speeds but almost a certainty. When I replaced the valve body before there was no burnt smell. Fluid was slightly darker then normal for what i would have expected to see. The old owner said it was changed under 3000 miles beforehand and I saw the paper work to back it up. The valve body I bought did say it was a factory updated version. I have no idea what they mean by that. When you go to shift it hits the detentes fine but the transmission itself doesnt go into gear. Have not gotten under it to see if it is actually manipulating the shift linkage on the transmission itself.