2024 Tahoe 6.2 with 4000 miles always use 91. Always been a touch rough at idle. Took in for free oil change and asked the dealership to look at idle. They said no codes and was ok. Reading around the forums it seems there is agreement the idle is set too low from the factory, maybe causing a slight lean “misfire”. Overthinking it I decided to try ethanol free 92, ethanol blend has an extra oxygen atom, leaning it further? It idles allot better on the non-ethanol. Not perfect but better.