Just finished doing some work on my 700r4, replaced the torque converter (made sure it was seated properly), the flex plate, trans filter and pan gaskets. When we replaced the TC and flex plate, the disconnected everything but the TV cable, simply because we couldn't disconnect it from bottom side.
Managed to get everything put back in and properly bolted, all fluids at the proper levels, etc. Yet for some reason, when I try to go into gear, every gear behaves like it's neutral. My buddy suspects it's the TV cable, but I'm curious if it might be something else?

 

No, the TV cable can't cause that.

First most likely thing I'd suspect is the converter bolts not put back. Seems hard to make that mistake but who knows, check it if you didn't physically screw them in yourself. Next would be pump damage from the converter not seated properly.

 

The bolts are in and torqued, did it myself. But I'm assuming if there is pump damage, there is no easy fix aside from rebuilding the trans?

 

I know of no such.

 

If you forgot the torque converter bolts it normally causes quite a racket from the flex plate rubbing the converter. You can pressure test the pump by either installing an inline pressure gauge in the trans cooler lines or pulling one off and placing in a drain pan then running the engine briefly. Low flow equates to a bad pump or broken pump drive, no real noise associated with shearing off the pump inputs when I have seen them happen.

Either way, the transmission is going to have to come back out, but on the positive side you've already done it once and it is easier the second go round. You also know that you have all the tools for it!