4 Wheel Drive/SUVs: 99 chevy auto 4x4 question, chevy pickups, auto 4x4

Question
Hi, we have a 99 chevy four wheel drive extended cab truck.  We have push button shifting ...into four wheel drive.  There is a option of "auto 4x4" which is suppose to engage four wheel drive when necessary......... in the summer we have it in 2 wheel drive but like to have the "auto" on in the fall/winter.........  this use to work like a charm but now it seems that when put it into "auto", it is engaged in 4 wheel drive all the time.... not just when the wheels slip..we had this checked last winter and spent quite a bit of money on a new switch.  They said it was fine but it just doesn't seem right still.

Answer
Jo , it could be the transfercae motor , or it could even be in the transfercase itself as well . There are alot of problems with the 4x4 in the chevy pickups. most of the time its either liek I say the motor , or the forks get worn in the transfer case causing it to act up . Thanks ADAM