I own a 2001 Excursion 42k miles, never abused but my 4x4 light has started to come on without moving the ****. Hubs are in auto mode, **** in 2WD, then out of the blue, 4x4 light comes on, if I slow down the truck goes into 4x4 and the only way to get the light out is to turn truck off then back on? Any ideas??