Take an AMP reading on the motor MT car down and see how close you are to full load AMP on name plate. It should be close to FLA with the problem your describing if it is not balance properly. But that is ALOT of weight to be off by if the car stalls with 800lbs or does it blow overloads? Either way drifting down with a brake pick tells you something is way out. Are you sure you have the original sling and platform? Cab ? I'm thinking your 2000 lbs off somewhere.