I have been using the dealer while still under warranty. If I were to take my 2021 LT Duramax Tahoe somewhere else and then I had a claim - even an unrelated one - I am afraid GM would try to wriggle out of its repair obligation. I am probably paying 50% more at the dealer's, but if I have trouble, I can honestly say to the service manager "no one has ever done anything with this engine except your mechanics". This engine is getting to be pretty common, but I am still going to wait for the warranty period to expire before I have my regular mechanics to do routine maintenance. Yes, I could change the oil myself and I probably will, just not for now.