Batteries are older and have been well loved. I don't mean babied. I mean well used. I did get an occasional cog. I figured that was the batteries having a hiccup. Yes it did seem quicker with the smaller pinion. If the batteries are on their last leg would it run hot with the larger pinion?
It was about 90 here today also. My ESC was much hotter than yours.
If that's so, it sounds like it was overgeared. I don't think the slash is "big" enough to require a larger motor, but that's just me I guess. I've also found in the past that better batteries (i.e. ones that don't drop voltage as much) will run the system cooler, since you're not trying to suck the life out of the battery and make power with the current. Packs that maintain their voltage level seem to run cooler.