So I'm going to drive down to Minneapolis and have a friend of mine who does Transmission work look at my 97 Thunderbird, but here's what's happening...
If I'm on part throttle, the car seems to sit at 2000 rpm as it accelerates, just kind of glides up until it spins up enough, this seems to be mostly in second gear.
Also, if I'm sitting at say 40mph in either 3rd or 4th, and nail the gas, the car will spin up to 3000rpm, but the transmission doesn't seem to downshift, and the car will very slowly accelerate while the engine spins to about 3500 over a few seconds, then grab 2nd and accelerate with gusto. If I manually downshift to 2nd and nail the gas, other than the minor delay from going from 4th or 3rd down to second, it just gets up and moves.
I'm going to drain and refill the transmission, and have him look at the internals. I do have a transmission cooler behind the radiator, big plate type unit, but as far as I know no J-mod or aftermarket accumulator springs.
Should I start looking for a later model Mustang transmission, or do you think it's a simple thing?