2000 Oldsmobile Bravada All wheel drive kicking in and out

I had the same problem with my 2002 Bravada. The AWD is engaged and the tires are all trying to turn at the same speed (not possible going around corners) so 2 tires start squeeling (skidding). I took it to the dealership and they told me the encoder on the AWD clutch moter was bad so they replaced it ($500). 2 days later it did the same thing so I brought it back and they told me that now the motor that engages the AWD clutch had gone bad ($200 more). $700 later problem Fixed.