Thunderdome, I'm not sure, but sounds like the radio slider
or speed control is dirty/worn on the upper settings?? But thats
just a guess on my part.. You may be able to see check the
radio... But sometimes it may be better to have someone
check it that has done it before.... But if your careful when
opening the radio, you could get a better picture of whats
causing your problem.. Now I said the above because you
said the motor runs on the lowest setting... Hope this helps!l

You may get more replies/help in the electric fourm...