Your story reminds me of my 15 HD 2500 Denali. Head Gasket ( duramax)went took 3 visits to dealer each time me telling them it is eating coolant to say it’s an HG! Duh! I am very meticulous about my stuff and the idea that a 70k truck needed this done was frightening as I don’t trust folks working on my stuff. The most concerning was they take the entire cab off to fix it! I asked the service manager to replace both sides while it was apart as I don’t want to come back. He said GM won’t pay them to do that but if it went bad they would fix it... well that makes sense
Anyway 30 days later I get truck back and sold it. Btw it had 50k on it.
I switched to a different brand and have had ZERO issues!!