No guys, it's not binding. If it were, there's no way that it would "coast" as far as it does. It actually seems to run pretty smoothly when the motor is getting electricity. (Mark, if you ran it a little slower we could tell for sure.) Almost 100% guaranteed this is SOMETHING with the electronics. Perhaps not the infamous magnetic ring, but something in the board stack, or the ancillary electronics for sound or smoke.
One last thought... is it possible that this big loco is overloading your Z-750 and tripping its circuit breaker? I would try once with the smoke off before taking it apart. BTW if you take the shell off and run it on the bench, please use eye protection. If the magnetic ring does let go, you wouldn't want any in your eye!
"You'll shoot your eye out!"