Slash is acting weird?? Motor or diff?? It runs, but it acts like its COGing real bad?? Only with a load on it? Somtimes is just studders? Then goes? If I put my foot in front of it,,it just cogs?? But the motor is spinning, slipper is moving? Truck has no real power....it should run up my leg..help its my sons, and I'm leaving in 2 days. I got another new vxl motor,, mabeee try that.