rick 12/3/2012The check engine light has nothing to do with it but have it checked some day . From what you say it would be one of two things . First . Might have the brake shoes on that wheel broke or the pins holding them broke and when you back up they get in a bind . If not then something in the gears in the rear diff is coming apart . Either way something should be making some kinda noise . The brakes will make a dragging noise or the rear diff will be grinding and or clunking . Oh one other thing . The park brake on that wheel may not be letting go . So when you back up it grabs and when you go forward the truck can power thru it .
erickkrotzer 3/22/2013Mine just did this. The rear wheel brake cylinder was not returning to center properly, causing the brake shoe to wedge when I backed up. Cheap but not a super easy fix. The wheel cylinder was surprisingly inexpensive, but all the brake lines were rusted like crazy. My father also has the same pickup and his did it too. I suspect it may be a common problem. You should be able to jack it up, spin the wheel in reverse, and feel the brake tighten up if this is the issue,