what causes my spur to be swiggly?

[blueb8llz]

this is for the rustler vxl. what i mean by swiggly is, when i give the truck some throttle, if you look at the spur meshing with the pinion gear, it looks like a snake. so the mesh is moving from left to right.
the spur does not wobble though. and i changed out the bearing that goes inside the spur. is it the bearings inside the tranny that i need to change, or is it the shaft where the spur goes onto bent????

and should i even worry about this? 2 spurs have been shredded within minutes, would this be the cause of this, or did i just do a bad mesh job? but the funny thing is, when i switched to a bigger pinion, the spur is not getting shredded. (but its still wiggly)