XMaxx upgrade your spur and pinion gear from wobbling and destroying itself. 

A must do to your xmaxx. . It will be your best investment on your XMaxx from tearing up your pinion and spur gears. Maybe you don't have to go 1.5 mod gears. Also upgrade your 7726 tie bar. I see they make them in SS.
(GPM Upgraded medium carbon steel cush drive input shaft and aluminum 7075-T6 bearing mount)
(Traxxas Part #7786X)