In my last post, I did the pump upgrade from Merchant's and then my 4WD quit working. I have checked the front axle actuator and it worked and I just finished replacing my encoder motor (easy to do, but really expensive) and my 4WD is still not working. I have cleaned the ground wires under the truck on the driver's side. I checked to see if I had power, the brown wire had 12V. When I put it into 4HI, it sounds like it is engaging. It will grind if I am over 25mph, and it will then sounds like it is slipping in. When I put it into 4LO, the transfer and tranny go into neutral. But I can hear it grinding as the truck rolls down the hill. It sounds like the teeth aren't catching in the front diff. or the transfer case. Checked the fluid and it looked fine. The idiot lights for my 4WD work and it doesn't throw any codes. I am utterly baffled. I depend on my 4WD system everyday, WHAT DO I DO NEXT???????????????????????

Finally got my 4WD fixed. The mechanic had put the slip forks in wrong. Everything works. Since I spent so much money on figuring out his screw up he bucked up and offered to put new tires on the wife's Expedition for no charge. Thanks for everyone's help and posts that had all the great tips of what to look for and how to fix most the problems.

Why did he have the forks out in the first place?

I wish that I knew. Probably a combination of not knowing what to do and being a dumba**. The second time around I gave him your instructions. Really appreciated the help with that.