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!!!!

Asked by for the 1998 GMC Jimmy
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!
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scan codes and post so we can adv