My 1998 F150 has just recently starting giving me trouble on switching in and out of 4WD. When I turn the switch to 4HI, I hear the switch making multiple "clicks" as if it is trying to lock in the front hubs. This last weekend, I was trying to drive up a muddy hill. After the switch appeared to lock in the 4WD (as shown on the dash light), I noticed that in fact there was no 4WD and I continued to struggle up the hill with only one back wheel spinning. Also, switching back to 2WD does not release the hubs as you can hear the linkage up front whine really bad as you increase speed. I've found that the only way to disengage the front hubs is to turn off the ignition and then restart the truck. It makes a couple of clicks and then the 4WD dash light goes out and I'm back to normal. Is this a symptom of a failing switch or are there problems up front in the hubs or somewhere else? Any help would be greatly appreciated.