trans problem.
 

hey i have a 250c transmission (M31). i just bought the truck. its a buick 231 and a 250 c in a mazda b2200. well i start it up, runs good, put into reverse or any drive ger, and the trans drags the motor down. i have tried lots of things. i even changed the trans filter and fluid. nothing. pulled pan again, disconnected the tcc, nothing. disconnected the brake booster, and plugged the vacume line there, still nothing. tried putting straight power to the tcc, still nothing. then i bought a new torque converter, and it still doing the same thing. it starts and runs good, but when i try to move it, its loke the tq converter locks up. it is snowing out now, so i pushed it out sede, and i started it, and put it in drive, and it didnt kill out, just started spinning the tires. im confused what is wrong? or what should i check next. about to buy a new trans, but am scared it is something simple and new trans will do the same.