Truck stalls and dies when in gear.

My truck dies when its in gear idling. It will
run good after i start it but the first stop i
come or slow down to. It dies unless i use
the two pedal method... Its a 94 chevy k
2500 and i just recently replaced the trans.
and the motor.  Cuz the last motor blew up
on me right after I replaced the trans.... I
replaced all my sensors on mynold motor
because it was doing the same thing and
finally died.... Im wondering could my
problem be a bad/ fried wiring harness?
Because the truck will run good with all my
sensors unplugged as far as idling and
starting. But wont idle or start with them
plugged in, and could. The stalling be a
torque converter issue? Any help would be
great. I'm a fairly decent mechanic and
haven't encountered much like this before
because I have replaced pretty much
everything besides the wiring harness and
running gear.