dash stated service four wheel drive, then it shifts to 4low

This is the second round of this happening in the last 4 years. I cannot find an underlying cause of why it keeps happening. I do not use my four wheel drive very much. The thing will start populating the service 4 wheel drive of and on, then with in 3 weeks when starting the car, it will be in 4 Low and cannot get it to switch to any other option. Sometimes it will feel like it is in 4Low, but other times it does not. When it does not feel like it is 4 low, when you stop and start it acts like it bogs down and is trying to shift. I would like to know why Chevy has no recall on this when I see that tons of people are having the same issue. I have had it repeatedly now. Chevy has lost my support.

I will NEVER buy a Chevy again! Had cracked heads due to loss of liquid, now the car goes into 4WD by it self! Electrical issues from day one. That should of been my first clue! I'm taking it in tomorrow AGAIN! My dash says SERVICE TIRE MONITOR and SERVICE 4WD. UG! Any thoughts?

Update from Jan 12, 2011: Took in the car... 5 new codes came up C0327/C0359/C0374/C0550...They fixed the Oil pan gasket,replaced new oil & filter, New Endoder sensor installed, new air filter sensing unit installed, plus labor $700 plus bucks> Car still makes rear noise like its going into 4WD again. Taking it back again tomorrow. UG!