Casey,
Truck rear 3rd members (pumpkins) are not universal. If the GMC rear has electric shift it's more than likely an Eaton, the rear in your truck is a Corporate GM rear, not the same.
Taking the rear out of a junk yard truck without knowing the gear ratio could be a BIG waste of time and money. Slide under the truck with a scraper and wire brush and find the stamped numbers on the front or top of the carrier housing or on the front end of the pinion shaft.
I'm confused...what's this "single one piece rim" you're talking about (22.5's are all single piece)?
Post some pictures so we can see what you have!
Mike B
