It works fine shifting into forward but about 1/2 the time when I try to reverse, it doesn't firmly go into gear. The props are turning in reverse very slowly though. If you give a bit more throttle it will sort of clunk into reverse (and then you are going faster than you want to). Sometimes when it hasn't 'caught' you can leave it in reverse a longer time and it will sort of catch in what I now call full reverse. In a nutshell, if it were a car I'd say the transmission slips in reverse. What would cause this?