1996 Ford Explorer Autosensing 4WD

I have owned my Explorer from the beginning and have done my best to keep it maintained. I would really like to hang on to it for another four years.

One problem I have had for several years is with the Autosensing 4WD. I think the 96 Explorer was the last year to have the 4WD selector switch mounted on the dash. This switch allows the driver to select from 2WD, 4WD Auto, and 4WD Lo. I usually have the switch selector switched to 2WD. When it snows and there is snow on the streets I switch the dial to 4WD auto before I put the truck in gear. I will then be able to feel the 4WD kick-in. Everything works well until I go over 30 Mph. If I go over 30 Mph with the selector set to 4WD Auto, the 4WD and 4WD Lo indicator lights on the dash start to flash. The only way to switch it off is to sut the truck off.

I have brought the truck in to shops and people tell me that my 4WD is working.

Any Ideas?
Thanks!