2002 Suburban 4WD issue

My 2002 Suburban has 215k miles. Today I put it into 4wd to back it up on to the ramps to replace the trailer hitch. When I drove it off the ramps, I attempted to put it in 2wd. After the 2wd light flashed for a while it went back to 4wd. I then tried putting it in Auto 4wd. Light came on but the truck was clearly still in 4wd. When I tried to put it back in 2wd from Auto 4wd, the Service 4WD light came on. I searched for the issue here before posting but didn't find anything specific to this issue. Any thoughts?

My 2002 Suburban has 215k miles. Today I put it into 4wd to back it up on to the ramps to replace the trailer hitch. When I drove it off the ramps, I attempted to put it in 2wd. After the 2wd light flashed for a while it went back to 4wd. I then tried putting it in Auto 4wd. Light came on but the truck was clearly still in 4wd. When I tried to put it back in 2wd from Auto 4wd, the Service 4WD light came on. I searched for the issue here before posting but didn't find anything specific to this issue. Any thoughts?

the encoder is stuck .. when did you last replace or check the transfer case fluid if not a blue color or low then that maybe the problem..

replace drive train fluids @40K miles. or when fluid turns dark .. blue is the color.

Transfer case fluid was changed 7k miles ago. Still plenty of fluid.
Just got my arm put in a cast so I guess I will try bringing it to my buddy's garage and pay him to change it. Thanks much for the help!
Bill