fragile spur gears???

[Gustav]

I think you need to gear up to more like the stock gearing if the motor is all that hot.What are the esc and battery temps like?
Edit:forgot about the big joes,the gearing squee suggested sounds about right in that case.

The heat is probably coming from the slipper slipping too much though,you need to tighten it down as much as possible,seems like your melting the spur gears.Probably the reason it doesn't do it at 70% epa is the slipper isn't slipping then.