Transmission problem

I have a 93 dakota with a 3.9 and A500 transmission I just had clutches put in it and now when i put in in reverse it wont back up. the tranny kicks into reverse but when you start to back up its like you put on the brakes if you try to give it gas. Idileing it will back up after the transmission warms up. But dont hit the gas or its stops!
It has drive second and first untill it warms up but then I lose drive it will shift from 1st to second but then just loses drive. And I cant get it above 25 miles per hour
Any body got any clues

just letting everyone know what the problem was. We pulled the transmission back out and tore it down and found a ring seal for the back clutch pack on the wrong grove. which was sending oil pressure to the torque when it wasnt suppose to.
So anbody rebuilding there own transmissions. (make sure you do the air test on the front and rear clutches) Before you put it back in the auto. This would of saved me plenty of bucks

oops!

Reminds me of the first time I rebuillt an A904... I mis-took "inch-pounds" for "foot pounds" and then of course the damn Dart wouldn't even move! Boy that was a long time ago.... and I still screw things up like that.... LOL! :)

That sucks!