My DHZ 140 with the 4 up tranny seems to go up through the gears ok (mostly) but when going down through the gears seems to find neutral and when it does find a gear it jumps into neutral when i accelerate? To get going again i have to come to a stop, get it into (actual) neutral, then start again. The motors fairly new so i dont really want to throw the whole lot out when it could be an easy fix. Any ideas?