Ok, it will reverse but only when the engine is rev'ed up some. This is a 2005 sierra. Auto transmission. I can feel it kick into reverse and it feels kind of grabby like it want to back up but it can't until I rev up the engine. Almost feels like I've got a bound up brake shoe but I've checked them all.

 

80 views and not a single person who wants to take a stab at this? Hmmm..