OK, maybe I'm missing something here since this is my first 4x4, but GM says I should be able to shift into 4HI while moving. Tried for two days now, it's real cold here so today I went out and drove for awhile to get everything all warmed up, still can't do it. 4x4 shifter is a manual on the floor shift. Shifts real smooth and easy while stopped, won't budge while moving (haven't tried hitting it with a hammer, yet). I tried while slowing down, speeding up, and going the same speed. Won't budge. Ideas?