[rotorwrench]

You mention that is pops out of gear while climbing a hill. While anything is possible, most problems I've encountered are related to moving down hill while engine braking. The thrust loads change from one direction to the other when moving from a fully loaded gear to a fully unloaded gear and engine braking makes it worse. Generally a loaded gear will stay engaged. I mention this from experience so I just want to clarify that it is slipping out of gear while fully loaded (climbing the hills).

Loose bearings and worn thrust surfaces can lead to this condition (allowing too much movement). Movement between the input shaft and the main shaft due to the internal bearing having wear problems or a bad pilot bearing could be a cause. The gear engagement dogs can end up with excessive wear as well but that shouldn't affect 2nd gear. There have been problems with some of the new bearings that fit inside the main input shaft.