88 automatic turbocouope,no power in gear

i bought a 88 turbocoupe that was sitting for about 6 months due to a bad a4ld trans.car only has reverse gear. someone took the computer out of it,so to get it started,we put in a 87 la2 manual computer so i could run the motor.well the car will rev free just fine(lots of rust chunks blowing out exahust)but when i put the car in reverse to go,motor cuts out power and car will not rev over idle when in the gas under load(falling on its face)is this maybe due to the manual ecm in the auto car?is there some clutch switch wire to the computer i need to unhook or hook up so the computer thinks the clutch is out?i just didnt want to go chasing other things if it was just due to the computer.oh,btw,the computer was hooked up in a manual car,and car drove down the road just fine under load,so i know the computer itself is good.any help would be appreciated.
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still has the same trans,im gonna put this motor and trans in a mustang,and wanted to make shure everything ran ok before i do the swap so i know if the problem was there before i do the motor swap.what its doing though is like the engine rev limiting the car.the engine loses power completely,so im shure its not to do with the trans the way it feels.