Turn on the electronics without starting the truck, and turn on the transmitter. Remove the air filter, and give it full throttle. If the throttle doesn't open fully, adjust your radio settings to allow for full throttle when the trigger is held down. You might have to adjust the throttle linkage so that you have the throttle open 1-1.5mm at idle, and fully open when the trigger is held down. Once everything is adjusted properly, reinstall the air filter and start the truck - if the rest of the truck is in good condition mechanically (no binding, clutch works properly, etc.) it should run properly. If it still runs slowly, check the clutch and slipper clutch assemblies for worn parts.
Founding member of the Solid Gold Racing Team - Mediocrity, redefined...
✯Jackson RC✯Horsham RC✯SJCCR✯