how do i locate and replace the 4wd sensor switch. on 1998 GMC Jimmy

it will shift into 4wd hi when slowing down from hwy speeds to under 45 mph. I then have to pull over shift it into nuetral push 2wd switch and return to drive then its fine. its annoying and sucking major gas. help!!!!

2 answers
There is a vacuum switch on top of the transfer case that is defective, replace it and problem solved!!
Just fixed mine, had the same thing going on. NAPA part # 7301639. Tough repair without a lift!!
Vacuum is what actuates 4x4 system!
scan codes and post so we can adv