If the dealer is such an ass, straight up tell GM you feel the dealers service dept broke your truck with improperly diagnosing it originally. Nobody else had a truck that undriveable from the update. Gm will reimburse your rental and probably offer a buyback if you keep saying you want a reliable resolution and have lost faith in the repairs done. When I lived in VA, and the dealers sucked, I’ve been offered a buyback over a clicking in my steering (2018 z71) saying I’m not confident in the ability and repairs of the dealers in my area. I was able to fix it with a bunch of red grease in the steering shaft knuckle. It was a custom order truck and I honestly just wanted it fixed.
pretty much, don’t ask for a buyback just tell them you don’t feel safe or confident in the repairs. I bet you’ll at least get a Silverado loaner.