another thing i did was i made the wheel axles from Taulman 910 nylon. PLA was too brittle when i really beat on the truck so nylon axles allowed flexibility from impact with the heavy tires on an object. the nylon shrank a good deal so i had to tap the 4mm screw hole after printing was completed. the shrink of the nylon and the tap left my wheel bolt very tight in addition i used the star washer, but i also had to go back and make my own wheel hex adapter to tighten the tolerance back up otherwise the PLA wheel hex slipped on the Nylon Axle Shaft.
no big deal just some quick work in Fusion 360 to get the revised parts out.
the small bevel gears in the axles and center gear case should be replaced with Nylon instead of PLA and i would recommend changing from the PLA filament for the Bevel gear shafts to 2mmx8mm Steel shafts. it takes extra work but you beef up the drivetrain.
print yourself a center skid plate also.https://www.thingiverse.com/thing:2764337
for fun i remixed some of the gears for use in a FWD i made. i may release it in the future.