burning out motors

ok, in the past ive had runs where the esc is 108, bat 95 and motor 170...but i didnt go for as long or as hard, maybe i was unusually rough on the truck...i really dont know, would running on loose gravel cause heat (spinning wheels?)

i was under the impression that a 9xl on 4s would stay cool...would dropping from a 20t pinion to say 18 make any kind of noticeable difference?...and im going to adjust the timing from normal to 0, but does timing make that big of a difference temp wise, i mean i need to drop like 88 degrees here!