2005 Blazer, 4.3, Auto, push button transfer case.
Won't always stay in 4x4H when going from 2x4H. Sometimes won't even select, shows in then drops out to 2x4H
Selects 4x4L okay
Any ideas?
Really need some help here.
Thanks in advance

 

The transfer case control modules (TCCMs) are known to fail on these. I had that problem. Look for threads on how the tccm works and how they fail with their symptoms.

Depending on what you mean by "dropping back into 2HI" you also could have a vacuum leak problem. Vacuum is what is used to remotely engage the front axle.