Ok, I just had a problem with my 2008 Silverado 2500HD the passenger door would not open from either handle. The door locks and unlocks. I was able to peel back the panel from the inside and used a mirror to check the connections. Everything was connected and it turns out the mechanism was stuck inside. I used a slim Jim kit to jam the end into the mechanism, right below the wire connection. While I pushed down on the Jim, I pulled the handle from inside, which opened the door. I jammed the Jim in so far I got it stuck. I unscrewed the mechanism and worked it out.
No matter how hard I would have pulled the wire, it wouldn’t have opened. Don’t damage the connections. Try to wedge something inside the mechanism. Once I removed it, it was obvious it was internal. Purchased a new one from oriellys and worked like a charm.