I bought a $500 dollar 91 RS with the 305 TBI and 700r4.

Previous owner stated that the car bottomed out and the reverse quit working. You can shift into reverse and feel the car engage but won't move. Also, while driving, if I go WOT running around 50-55, the car revs up but doesn't accel. From what I have read and seen, the TV cable appears to be adjusted correctly. It acts as if it is trying to shift down and catch 3rd, but almost like it isn't there.

Is this going to be a complete rebuild, or does it sound like something simplier. The car was low on tranny fluid and had sat for a while when I bought it. I drove it home and got the fluids all topped off, but it has not helped the transmission.

I'm buying a new battery probably this weekend and will give her one last test run.

I am planning on a 350 swap in the future, as this is my play car. But needing to know whether I'm spending $100 on the transmission or $800 is going to determine my timeframe.

It might be the final run for that tranny indeed. Anyway, from what you described along with the purchase price of the vehicle, it sounds like it's time for a rebuild. Drop the pan and check for heavy amounts of metal shavings.