Success at last!! Still a couple of 16016 ???s

[Batfish]

When you go from throttle directly to neutral, the MGM will freewheel no matter the programming options. It sounds like you're freewheel option is "off" and you may just be going right to neutral sometimes, but move to different throttle speeds other times.
If you don't already have one, put a fan on the motor and see if that drops the temps below 180F. If it does, I wouldn't worry about the gearing. If you already have a fan, consider dropping one or two teeth on the pinion.
Your setup should definitely run hotter on the track than on the street.

By the way - great to hear that you got the truck going and that (almost) everything is working great! :)