The whole truck doesn’t need to be disassembled just the engine removed to check for a bad clutch bearing or a broken spring which if it is one of these things it will cause the issue you are having. It could be a tuning issue but I can’t see and hear the engine. Do you have a local hobby shop near you that could look at it? The thing about these little cars is that they require maintenance and stuff will break. These little nitro engines require tweaks in their tune depending on the weather etc so it’s important to learn the basics. I don’t know what region you live in but it’s pretty cold out now and these little engines can be quite finicky in the cold and don’t like to hold a tune.