Do you fluctuate between regular and premium? I can’t speak on the 5.3l, but I can say for the 6.2l (2011 and 2020 Denalis) it should be fed premium. I notice the change when my wife is driving and accidentally fills up with something other than premium. Since I bought her that turbo, she hasn’t made that mistake because her car now takes prem as well.
mines the oddball, it's a aluminium 6.0L. so not the 6.2 rectangle port heads, they are lower flowing heads, the Cathedral port ones. I read they have better air speed at lower lift. I don't remember the number on them but basically the ls1/2 style head. basically they fill the cyl better at low rpm but give up hp to the 6.2 head up top.
the cam is a weird one too, it's a hybrid thing, not as good as the prius twin cam setup where it can control the timing of both cams separately, but it's the pushrod version, late intake valve closing grind. basically it bleeds off cyl pressure a bit at low rpm, giving up tq off idle for efficiency in the higher rpm band, higher being like 2k. so to over come that it does have a higher compression ratio than the normal trucks, but it still doesn't call for 93 because it bleeds that off and the tranny doesn't ask for power at low rpm. peak tq is usually where you need higher octane. it's got electric motors for low speed and the tranny let's it set in the efficiency range of the cam and basically acts like a cvt pulling the truck along without the rpms needing to rise and fall. think of it as you're requesting how fast you want the truck to go with the throttle pedal and it doesn't a bunch of clever things to give it to you. feels completely different than a standard auto switching thru gears but not like a true cvt either. since those have zero tow rating. to me it feels like a huge thing that just glides down the road without feeling like it puts any effort into it. it's even different than my electric car feels. those feel more directly tied to the throttle pedal, these almost ever so slightly feels like a turbo car without the lag.
yeah I know, to much haha. but yeah. it's different to say the least. some people have said they have seen a mpg more on 93 than 87. but I'm not sure it's true, cause why would it be if they put that much effort to run 87 plus it's over a 1$ more a gal. take a lot more than a mpg to offset 4$ vs 3$ a gal in a daily driver that never even sees half throttle.