Engine/Transmission (1998.5 - 2002) 4WD auto engaging

[PHellums]

I was hog huntin this weekend at spent all of two days in 4WD mode. When we went to leave for the house I put the 4wd shifter back into 2wd and everything went smoothly into gear. When I got to about 20 mph the 4wd light came back on and I could feel it engage back to 4WD. Slowed down to stop and when it got below 20 it disengaged again. Stopped the truck, put the shifter back into 4 HI and put it back to 2WD. Did this over and over with no change in outcome. By the way, truck is an '01 2500 auto. Need all the help possible. Thanks

 

[PHellums]

Fixed it!!

Got a chance to climb under the truck after work today and found that one of the vacuum lines had gotten pulled off somehow. Put it back on and it works perfectly.