I appreciate all the feedback - I need to get the other engines out tomorrow and test it - I didn't have time this evening to get it all out as I was troubleshooting low track voltage issues (which I have resolved and didn't solve the problem).
On another note, it's interesting the comment about the battery. I'm wondering if the battery has some problems as my engine is from 2008, and I've never replaced it. It seems to lag at times on the track, though it never loses its connection with my iPhone, and it never stops running. I was already thinking about replacing the battery anyway, so I will try that and see what happens... it'll be a few days before I can do that as I'll need to order one.