2001 Chevy Blazer Problem with 4WD

Other Category problem
2001 Chevy Blazer Four Wheel Drive 150000 miles

I have a 2001 chevy Blazer that has the 4 button switch in the dash. For some reason it keeps shifting possitions all by itself. Sometimes it shifts into 4wd low, sometimes it shifts into 4wd hi, sometimes into 4wd auto matic. It even shifts into 4wd auto. & 4wd hi wwhile I am driving down the road. I took it to the chevy dealer they put a new switch in and it got better for a while. Now it does it every time I drive it. Do you have any idea what the problem might be & how to fix it. It also does not want to shift back to 2 wd hi very easy. I have to keep bushing different buttons to get it to finally switch. But sometimes it shifts perrfect.