Another junkyard rescue

[65standard]

I just saved this 1985 C10 SWB from the junkyard. The only thing wrong with it is the transmission. It will not shift out of first unless I manually down shift it, then manually up shift it. It is a nicely optioned truck and didn't want to see it scrapped. It looks like a standard turbo 350 trans without any computer or TV cable.

My question is what are my fix options. I'm hoping it isn't anything mechanically wrong with the trans. And maybe it is just the vacuum line or the electrical connector on the vacuum line for the shift module.