Rear left door sensor intermitantly thinks the door is ajar. on 2008 Chevrolet Silverado 2500 HD

Whenever the truck goes over a bump in the road the rear left door sensor indicates that the door is ajar - which it is not. The automatic step starts to come down. I am on a trip with my daughter and it's driving me crazy!!!

You cold have a problem with a doorjamb switch or connector or a wiring problem. Get it checked out by a Chevy specialist.
If you want to find a GM specialist, here's our directory link for you: