Ok, so I've pulled the motor off and thoroughly checked everything. I can't find any damage whatsoever to anything.
I called Traxxas and was told to simply loosen the screws that bolt the engine to the mount, then shift it forward and retighten the screws. I told the guy I spoke to that I didn't think there was enough play in those holes to do that, but he assured me there was. So I give that a try and sure enough there is absolutely zero play. I couldn't move the engine forward or back at all.
Now I'm starting to think there's a defective part somewhere. I'm even wondering if the holes on the engine mount were drilled too far back?? Anyone have any other ideas?