99 Ford Expedition 4x4 no-mans land HELP!

This is the latest in a series of issues my truck is having. The 4x4 light is blinking, even when the truck is in AWD. When I make a U-turn, the wheels sound like they are grinding. When I put the truck into reverse, I usually feel a sudden slip followed by a clunk and grind - like the transmission is slipping or I am going into 4 wheel low. The transmission is only 2 years old and I just had the belt and alternator fixed and new tires put on. Brakes were done recently and that rusted out wheel bar thing (non-technical term) that holds the back end up was also replaced. Does this sound like another major problem?? There is only about 130K on the truck. Oh - and man is she sluggish going up hills. I mean REAL bad on hills and bad on acceleration. Please help!! THANK YOU!!