Dies when put into 1st or reverse

92 mustang when I changed motor I put another t5 I had in because the one in the car was failing. This being the 2nd trans. The 2nd trans was acting like this also,when put into 1st or reverse or down shifting it would pull the motor down to almost die or all the way and die. 2nd trans started failing so I installed a 3rd trans that was suposed to be rebuilt, it did not act like that. Did not pull motor down when put into gear at all, how ever 2nd gear did not work. So I bought a new TKO 500, installed it and it pulls the motor down when put in to gear or down shift. I'm thinking the problem is in the trans some where because the 3rd one did not act like this. Any ideals?

Definitely not a tranny expert,but sounds like something is putting pressure on first/reverse gear and pressing against back of crankshaft. If thats true,better be checking thrust bearing in engine.

just a thought, do you have the correct pilot bushing

There are 3 sets of wires that plug into trans, one goes to speedo grear, 2nd toreverse lights, 3rd to neutral safety. I started unpluging them one by one and starting car and putting it in gear, when I unpluged the neutral safety it was fine,did'nt pull motor down. Not sure what this means, maby wires are backwards?