All,
Thanks for the help. I checked the tender wheels and they all seem to be aligned properly, so short is unlikely to be my problem. The overloading seems like a plausible cause, because at some point there was a click in the Power Pack unit after which it wasn't working for about 15 minutes - I figured protection circuit kicked in. What you grumpy saying makes sense, although I'm disappointed I won't know for sure until I get a more powerful Power Pack. I'm thinking to go with the Digitrax Zephyr. I'll stop by the shop this Saturday and let you guys know. I would hate to find J Class to be defective and have it return.

On a side note, I was surprised there were no manual, notes for the actual loco in the box. There was online manual for the Soundtraxx DCC controller and schematics. But I'm not even sure how to uncouple loco from the tender. Do I just unscrew the bottom plate from the tender to free the connecting rod?   

I recently bought a Bachmann Explorer DC Starter Set with a Baldwin 2-8-0 Santa Fe locomotive. This runs just fine. I just acquired new J Class locomotive with DCC Sound; Really awesome piece of work. The problem started after running  J engine with 3 lighted cars from Santa Fe set: after 15 minutes or so of uninterrupted going around the track, engine suddenly stopped with sound and lights momentarily off. Immediately, sound and light come back on as if engine just getting started and off she goes. Sometimes when this happens locomotive lights flash 11 times (I think) which in the manual indicated a motor lead short. However all the time it happened cars appear to remain lighted.
Track is being powered by the included DC Master Power pack from the set. After having it happen about a dozen times I removed J locomotive of fear that I can get it damaged. I put Baldwin engine back on track and it runs with no problem. Do you guys have any suggestions as to what going on? Do I have a defective J Class? Any help would be greatly appreciated.

Thanks.