I know this is an older thread. But, I'm having the same trouble. I cut firewood in a hilly timber. I also chain logs and drag them to a clearing to cut up. I got stuck 2 times and had to call my dad and brother to pull me out.
So, I'll be checking these plastic vacuum lines, and then if they are fine. I could expect it to be shift motor.
It seems to work fine once I make it to the road, but in the timber not working. I can feel it shift, but no front axle action.
Thanks all for the info, I actually found this thread doing a search.
Has anyone changed a shift motor? How hard is it? My truck is 2003 f150 Lariat.