I bought an AF SP U33C and it works great. This is the first AF TMCC or Legacy engine in a long time that so far has not required any repair, tweak, workaround, or modification to get it running well. The only shortcoming is that the "Southern Pacific" lettering on the left side of the body is not level, but instead slopes down toward the rear of the engine -- the handrail beneath it calls this out nicely. The lettering on the right side, however, is level. So close to completely correct, but not quite. The one "tweak" I made was to change the setting from pulmor diesel to diesel in order to get 3 levels of smoke control, but apparently Legacy 1.4 takes care of that. I just have to get around to buying a black fob, downloading, and updating. One other observation - - the last 2 AF Legacy engines I bought have worked reasonably well as opposed to completely inoperable - - but those came to my house via UPS; the last two I brought home from York and a dealer's store. Hmmmmm.
I guess I've led a charmed existence as I haven't had any inoperable Legacy engines to speak of-just some cosmetic shipping damage (loose parts). My U33C ran well out of the box as well; my only issue was the little China-person that installed the body on the chassis used a power screw-driver and cross-threaded three screws. One screw would not pull down tight and made the body set askew on the frame until I figured out what was wrong. One of the brass inserts actually came out of the body trying to get the body off the frame.
So far, a U33C and two challengers...all good. I hope that continues, a have some of the SD70s and two more U33s on the way.
Will the 2nd run of the U33C's have two motors like the SD70ACe?
I wouldn't bet on Lionel re-engineering the drive in the U-33C - it took too long getting that one to fit the chassis.