Octane rating needed is only to prevent knocking. So if you put 92 in a truck that only needs 87 to prevent knocking your wasting your money. The issue with modern cars is they have knock sensors. When your truck starts to knock it retards the timing to stop the knocking as it is very harmful to your engine. That also loses power. So your truck runs correctly and optimally with 92 octane. Its tuned for it. It is the most efficient with it. When you put a lower octane in it....you may not realize it due to the knock sensors, but its knocking....so your computer will adjust the tuning to try to prevent the knocking. It can only do it to a certain point. Knocking is detonation. That is an engine killer. Can you get away with a trip on 87 no load, not towing, no high heat.??...yes. Its not good to do. In the old days when we did this on a non computer vehicle you heard quite alot of knocking...which is damage. Your truck is designed and tuned for ONLY 92.
On a side note I feel your pain. I had a 2017 Denali, but the older generation got pretty good mileage. I routinely got 22-23 hwy. It was unforgiving if you floored it though. We went to buy a 2021 Denali, did the test drive, loved it. I was really surprised the mileage went down. Then spoke and read up that it was even worse than that. ??? I dont know what GM did, but it was a deal breaker for me. Then the lifter issue arose. We rented a '21 suburban for a month and the mileage was very good in the 5.3. I just dont want a 5.3 at that price point. The 3.0 was what I needed for towing and normal mileage. Early on they werent around yet, so we bought the Denali CC with 3.0. its our in-between truck till this insanity stops. Mileage is insane, torque is fantastic, tows great. So our next Yukon Denali will have the 3.0. Loved the speed and power of the 6.2 but todays version has unacceptable mileage. Hopefully prices come down, but I would run 92 if i owned it. Good luck
