I run 19t pinion 87t spur dont think it is under or overgeared on 2s 7.4v ... my e-firestorm 2wd stadium truck complete with battery/body into it is about 5lbs... esc are like about 120 to 130f and motor 180 to 195f ... battery are cooler ...
Have you tried a 25t pinion ? according to your thread the highest you went was 19, I run 30/74 on a similar setup and it only gets hot after long runs because its overgeared