take out your motor, try if it works withtout load (no full throttle though!)
maybe check your settings, if you do not have current("power") limiter set and your ESC just does not allow enough current for the motor, but I doubt this

try whether you cars moves without the motor, eg it rolls freely, wheels spin easily.. if no, check bearings, one non working bearing may pretty much stop your car. if they are ok, check individually the diffs, meaning test each one individually, if it you find one that is stuck, most probably your center diff, if you say it is making noises, you have to look inside.

you can also check your pinion/spur mesh, if too tight, it could potentially block the car.