The 783 Hudson! Puller or slug?

I bought a 783 Hudson that was new in box, it is a very nice loco. I have tuned it up from info that I've gained on here and the other forum. I've add shims, moved magnets, lubed it, and even ground the ends of the rods down.  I've ran this engine to break it in; don't know if long enough: several hours for sure. it runs some what better but; It still seems like a slug. I have a consist of 7 aluminum passenger cars; all have been cleaned and oiled; that I like to pull with it. I have a good ZW with great voltage,so no issues there: although I have to operate the ZW wide open for very little speed. I can hook up a freight consist of MPC and Modern cars; even with the free rollin trucks, still a slug. Are they really that bad, for such a nice engine. Is there any more suggestions. Any body else have one that snail paces along, and an ant could out pull. How many cars dose yours pull, how mant passenger/ freight cars do you suggest?