eye one

My LST will pop out of gear and I dont know why. It's definately the hi-lo shifter, it doesn't want to stay in gear. I have taken the tranny apart, all looks fine. Putting it back, it seems fine. If I switch it to hi it runs for a little, then it goes to nuetral just after I turn and then it wants to go in low gear. When I had the tranny apart I checked to see that the shift fork is inserted in the lever correctly and it is, but it doesn't seem to stay put when it's running.

I cant figure this out, I know there is all of 3-4 mm of travel with the selector and it moves just enough to slip out of gear. Never had this problem, and I dont even use lo gear.

Suggestions???