Recently had a local shop swap in a used 2.8 into my already 2.8 RS that had thrown a rod. (Should've just spent the money on adding 2 cylinders, i know)
Prior to leaving it at the shop and before it threw a rod, the transmission ran perfectly fine and never had any slipping of any sort.
Shop told me they had the motor in, but while "test driving" it, apparently they figured i needed a new transmission too, due to lack of functionality. After test driving it, seeing it was in good enough shape to drive onto a trailer, I paid to get my car back in the condition it was in.

Condition being... It will drive in 1st gear fine, but hates to get into any other gear, It will rev high and not upshift, although I have once or twice gotten it to get into second but nowhere near the speed it should be shifting at. Couldn't get it up to speed at all.

I've done a tiny amount of research and read that it could be the TV cable, and am of course going to try that, but I thought it'd ask what any and all issues could be causing this? I'm aware a rebuild could be around the corner and am not afraid to drop the tranny should need be.

I'll attach pictures of my tv cable and bay

 

Probably misadjusted TV cable. Pretty simple but most "mechanics" are completely baffled by something with 1 button you press to automatically adjust it.

Hopefully the trans clutches haven't been totally fried by now from it being driven while misadjusted.

 

just adjusted it. (pic 1)seems the cable assembly came a little farther out from the mounting tab than where it was before (pic 2)

Cant test drive tonight but will update tomorrow

also noticed there was a few washers stacked where the mounting bracket meets the intake plenum. would this cause any interference with the tv cables adjustment? (pic 2)