Stuck in 4 high

What is your question?

My 2008 GMC Envoy is stuck in 4 high. When I turn the 4x4 knob to 2 low it automatically sets it back at 4 high unless I put it in AUTO. how do I fix this?

What makes this problem better or worse?

Putting 4x4 knob at either AUTO OR 4 high.

How long has your 2008 GMC Envoy had this problem?

Months