98 Passport - 4WD Not Disengaging Consistently

Lately, the 4WD has not been disengaging consistenly when I hit the button to turn it off. It engages fine and works fine when it's in 4WD. But when I am turning it off, the light sits there and blinks for a really long time--and sometimes it does not turn off at all until I stop or brake/slow down a lot.
Noticed it a couple times today going to and coming back from work in the snow . . . was really crappy here and there, so I went into and out of 4WD a few times.

Any thoughts? In the past, it has taken longer sometimes for the 4WD to turn off--but never as long as today. Is there something I could check to see if three is an isuue? I never drive in 4WD above 50mph--the manual says it's ok to do so up to 65 but I never come close to that so not sure what might be going on.

Currently have 150k miles, have recently had the fluid all changed so everything should be good there.