Service 4WD

Just wondering if anyone has had this issue and what the outcome has been. I have a 2002 GMC Yukon. You can drive all summer in 2wd and no issues. Engage 4wd and sometimes a mile, sometimes 5 miles down the road and the service 4wd light comes on. Also, the dash switch lights go out. The problem is usually cleared by restarting and being able to shift back into 2 HI. Luckily we also have a silverado with working 4wd so I have swapped some parts. I've swapped the switch and transfer case shift motor and no dice. I was hoping for a quick not having to go to garage for scan fix but I guess that's not happening. Anyone else have these symptoms and what was the resolve?