I push auto 4 wheel 4 high 4 low they all just flash

I have a 2002 Blazer with the same problem. A mechanic told me that sometimes the electronics need to be reset, I forget which component specifically. Just disconnecting the battery completely, and touching the leads together to discharge capacitors and such will shut everything down, and when it restarts, hopefully it works again. Mine did. My symptoms were that whenever the 4x4 lo or hi button was pressed, both lo and hi lights flashed for a bit, and 4 lo or 2 hi (never 4 hi) engaged, whatever the system wanted to do at the time I guess. Yours sounds similar. Anyway, try it out, its free and simple.