Pretty sure the GM computer is just slow. Jaime used a relatively high end diagnostic tool and also had issues with data rate. I'm dying to try my Snap-On Ethos Pro on one of them. Just haven't had the opportunity.

Concerning premium, BE OBJECTIVE AND SCIENTIFIC! Most engines will not benefit from 91 octane UNLESS they say it is "RECOMMENDED" or "REQUIRED" - obviously, in the case of required, you should do it no matter what.

The ENERGY CONTENT of the two fuels is almost identical. The idea that 91 octane fuel will get you a 27% increase in mpg is completely and utterly absurd. If you track your mileage and driving habits, you will find that vehicles designed to run on 87 octane will NOT achieve any greater mpg on 91 octane. The only thing you'll ever get out of it is a lighter wallet per mile traveled.

Tahoe_08 suffers from confirmation bias. He wants to believe it works, so he believes it does. If his numbers are legit, and I wouldn't believe it one bit, unless he had detailed mileage records over a very long period of time with climate data and other variables reported.

Don't trust me? Google it. You will find countless articles debunking the myth. Tom (RIP) and Ray (Car Talk) chime in on it too:

https://www.cartalk.com/content/premium-vs-regular-0

Please do your research before you wipe your butt with your money.

 

i all ready tried 87 for a while it always seems to downshift to 3rd gear on the up hill.

it was noticeable after using 91 oct for a while and when Shell gave me 87 oct (from the 91pump a bit over 9 gallons) there was clearly a difference in power.. this was confirmed with the timing table dropping to negative -10_+10 range in v8 mode... and v4 no longer worked at all...(flip flopping between v4 and v8 every 1 second) i'm pretty sure the rapid cycling of the AFM. is not good for the engine or components
it dropped back to 18.5. if your willing to put up the extra 1.23 it cost to run 87 i'd be willing to run 87 for a while ...

also the EPA is 21MPG on the Tahoe H so getting 23MPG is not too far fetched.. since more then likely the 91oct is still on summer fuel while the 87 tank is on winter fuel

 

Thanks. My understanding is that at one time you had to buy the 91 in order to get the cleaning detergent additives in the fuel, not now they all have them at my costco.

I had an Acura MDX in the early 2000s. It said USE premium gas only. The 1st year I spent experimenting with 91 and 87 because my dad said "it won't make a difference". I drove the same route as a sales rep so the terrain and conditions were identical on the tanks. It never amounted to more than a 1 mpg swing at most 19-20 mpg and most tanks no difference. So I saved my money and used 87 for the next 8 years and 191k miles. That's about 10,000 gallons at about $1-$1.25 per, I saved $10-12,000 dollars.

I was thinking since I have never had a ride that switched from V8 to V4, I would see how it did on next weeks trip with a few tanks. It will have way more variables of terrain and weather in each tank so it will not be an accurate read for mileage but may show something on the V8 to V4 switching or not. I have driven for 18 months on 87 and never noticed a significant swapping from V8 to V4 at highway cruising speeds. I only see it on uphill climbs which is to be expected.

Stay tuned. I will let you know what I find.

 

Well I Hypermile as it's called makes quite the difference.... We have much higher speeds most posted limits between 65MPH and 40MPH and 45 -50 being the most common
This is in the city..


considering the suburban 6.0L barely gets 13-14 combined i think we are doing pretty good

small cars command quite a premium in California (gas prices) plus i don;t want to be in a small car when someone t-bones me at 65MPH this nearly happened too many times all ready with my old car (others running red lights or stop signs)
and many many times with this SUV,, 18wheeler impeded my right of way(was going 55 at the time barely was able to stop in time almost made contact with in a 2-3 inches of my driverside A pillar, i almost slipped under the trailer contacting the rear drive wheels as the trailer was still at an angle)....I was able to get in front on him and impeded his path and make him waste 30min I went like 5mph it was a construction zone anyway they had just scrapped at the asphalt as they were Redoing the job the second time since the previous surface failed with in 2-3 years as they did a sloppy job
and i did not want to pop the tires or blow the shocks..anyways...


I had to becareful as two of my wheels were in the dirt and if you stop FAST BAD things happen (you lose control Ez)

I have all ready been rear ended by a driver all ready once before in my old car

another person tried insurance fraud me but failed... mutual backup incident but he tried claiming the damage on his New prius was caused by my SUV (Location of the claimed damage did not meet any spot my SUV) I lied to him and said i had a dash camera and his 3 fairy tail stories, he gave me was on camera and VOICE recorded.. he immediately left....

he tried claiming immediately he and his 5 passengers were injured... how the f do you get injured from 2mph hit, if i hit a pedestrian @ 2mph it would just scoot or nudge them out of the way XD


to top that off the next day mind you another person tired pulling the same EXACT scam, another car... I had my horn ready as I had spotted them conveniently waiting inside the car directly behind me , so they can leave at the same time ... they started the car at the same time they started moving at the same time as me

I laid down the horn :O


For some reason I have became other peoples Primary target for insurance fraud

maybe it's because of the hybrid thing and they think it's rare so it must have cost more ???