Any GM 5 speed auto trans from 1987 to 1995 should fit. Make sure you fill the torque converter. If you want more thrust as take-off get yourself a racing torque converter.
would suggest going to b and m's website- that have some pretty awesom trans- you culd go with an 4l60e but you will need the computer to go with it....could go with a turbo 400 and a gear venders overdrive unit- thats would i use....gets awesome fuel milage