Something else that might help is to replace the center set of wheels in the passenger cars if they have a 3 wheel set-up, as the center set of wheels is usually plastic. Lionel post war and Williams Crown Edition axles will fit together pretty good, just replace the whole axle and wheel assembly with a Lionel post war one and you will have metal wheels instead of plastic.
I have upgraded a Williams SD-45 with plastic non-flanged wheels to metal wheels and got rid of a stalling problem.
Lee Fritz