Hi Jim,
It's been a few years, but Dave Laughridge, aka Dr. Tinker, did some great work on a couple pre-war pieces for me some time back. You can find him by doing a quick google search. Since the Classics version is essentially a prewar repro, right down to the motor design, I would think he can help.
Regarding your problem, I had a pre-war O gauge 248 that did the same thing, but after a rebuild and rewire, it ran like a charm. I'm curious about your 390E, as I've got one as well, although I haven't encountered a similar issue... yet.