In a Case like this its process of elimination.
Start at the Begining of the line. Make sure Servo is moving the Throttle, make sure Carb is doing what it should, Like Jamxx said is the Engine Revin up? Then move further down the driveline to the Gears, then to the Clutch, then to the Differential...Possibly even your CV joints. I know I thought I blew all my gears B4 but after closer inspection it was just a loose CV joint, therefore all the power went to the one Wheel that wasnt spinning. There arent to many compnents on an RC, eliminate what ya can