Reply to "GP-7 poor performance"

I do not know if this helps, but I too was having problems with one of my LC locos pulling some of my cars with out slipping. I had 4 post war cars (empty gondola, 2 Sunoco 2 dome tank cars, an empty cattle car and Caboose).  Turned out it was my postwar Caboose.  One of the axles on the rear trucks was binding, It was would turn some and then it wouldn't , like the bearings were seizing up except it has no bearings. I replaced the trucks and now my train works great. Just my 2 cents