2wd shiffting to 4 high wheel drive

What is your question?

I put a new 4wd actuator in my 2001 Tahoe. It will shift from 2wd to auto 4wd. I hear it clunk into gear but when I put it in neutral and try and switch from 2wd to high or low 4wd it thinks for a second and goes back to 2wd and I get a light on dash that says service 4wd. Now another thing that is relevant is in the spring of 2018 I got my Tahoe stuck in some mud mostly water that cam almost into the front driver side door.

What makes this problem better or worse?

nothing

How long has your 2001 Chevrolet Tahoe had this problem?

Shifting down to 4 low 8 months