oneslowlx91

I have a 5.0 91 lx mustang with some work done to it. I have heads, cam, intake, injectors, 3.73 gears, fuel pump,cold air, maf, aod transmission rebuilt, and that is about all the "big" things i can think of. now this is were i get confused. The car just came out of the transmission shop and drives fine, shifts fine and down shifts fine. The car moves out very well if i do the "maunally shift" with the aod from a stand still. now when im just driving along at 25 mph and smash on the gas the car goes no were. I dont know if that has to do with the trans having a problem, the car just is not fast or what. If anyone can tell me if i need to take it to the trans shop again and have them rip it out or that is just how the car is.
thanks