I was driving to work this morning when all of a sudden the engine began revving and I was slowing down as if the clutch disappeared. No noise from below, no clunking or other telltale signs from a angry transfer case. I rolled to a stop on the side of the road and placed the truck in park and turned it off, back on again and rotated through the gears. Nothing, just as if the engine was freewheeling. I tried engaging the 4WD, reverse, everything..but still nothing. Do I have a clutch issue or it is a linkage issue?