First off, will the clutchbell/pinion gear rotate freely with the engine off? No,definite clutch problem. Either the clutch shoes are bound up or the bearings are shot or both. Yes, you still need to pull the clutch bell off and check for a broken spring on a clutch shoe. No spring problems, sounds like a tuning issue.

Second, the idle speed may just be too high. do you know where the idle screw is? Counter clockwise to slow it down. if you don't have a manual you can download one here and also just do a search on tuning guides. There are several around.

Third, even though it is a Losi knock off, the parts and procedures should be similar enough to get help under the Losi truck thread. Good luck.