In the driveway or on the street or whatever, it shifts into low range easily and smoothly. But when I'm on the trail, it won't budge from High. I can't get it into neutral either. It just shifts between Hi unlocked and Hi locked.

I've tried rolling forward, rolling back, finding level ground, putting it in reverse and backing up a distance, park, neutral, drive... it always seems to act up at the top of a steep descent when I need low range. I end up riding the brakes down the hill in 1st high. Or it will act up at the bottom of a steep ascent and I end up lugging the motor and slipping the torque converter up the hill. Then when I get home, it shifts into low very smoothly.

 

You need to shift into lo before you need it, with the strain on the driveline of sitting ontop of a hill it will be hard to shift.