I've had several different maladys with my tractor over the years but never your problem. I've had shift fork problems with my 4wd a few times and had to replace the fork a couple of times, but that can be done by draining the hydraulic oil and the shifter/fork assy unbolts from the side of the case easily. I don't recall the shifter configuration on the range trans but maybe it can be removed similarly - has been awhile since I was under mine. The 4wd shift fork is easy to bend, I treat mine very gently nowadays, maybe it's just a matter of replacing a fork. The range shifter has a pretty healthy stick on it and sometimes mine has to be played with a little to shift into the 3 different ranges, I go easy with it, sometimes have to rock it back n' forth a little.