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Consider the Yukon Denali and Yukon XL Denali and the Tahoe Premier or High Country and Suburban Premier or High Country. These are full frame trucks built for towing and comfort and will still be on the road 20+ years from now faithfully serving their owners. These do not share the spartan...

It's been the best for my vehicles. Even the 1990s versions lasted 80-100K miles and delivered outstanding wet weather performance.

It's been almost 2 years since your last post on this topic. What did you ultimately purchase?

Lubricity is greatly diminished after about 5,000 miles, regular or synthetic. Rub new oil between your fingers and some of that old oil between your fingers. Which do you think your engine prefers?

Yep, I buy only GMCs, Cadillacs, Buicks and Oldsmobiles and Pontiacs! ;)

Yeah, it's great. I always tell folks that E85 is like cheap race gas. We didn't have it thirty years ago when I was racing.

This was in the 1990s. I would run it daily for one week a year when I took the car to Bowling Green, Kentucky for the annual GS Nationals. We often ran 100 unleaded or VP racing fuels all weekend long in town when we were dumb and street racing. I had a drawer full of new O2 sensors for each...

I used to run Sunoco's 104 unleaded in my Buicks. That increased fuel efficiency even more and the motor loved the stuff. It of course ran faster in the quarter mile, ran 4 degrees cooler and idled more smoothly as well. Great stuff! My truck on E85 behaves the same way except for the gas mileage!

How can there not? Different additive packs for starters. For more than ten years, I would always count on Shell's 93 to deliver 2 mpg less than Mobil's 93. Cumberland Farms was even worse. I paid a lot of attention to brands back in the '80s and early '90s. Then settled in to just using 93...

That's a direct injection motor right? That was my one caveat. I challenged a guy on another forum a few years back and he proved me wrong with the 5.3 in his Chevrolet Tahoe. But he does see differences in fuel economy by brand, as I have.

Have you run and maybe documented such yourself? I've never seen this to be true excepting DI engines and even they see differences in efficiency between brands of fuel even.

Well, today it resides in my head. I threw away all the little note pads from the cars a few years ago when cleaning out the garage. I do however have detailed logs in excel spreadsheets for my two trucks. Right after purchasing the Yukon, I ran a couple of tanks of 87 and she ran like crap...

That's quite revealing man. Thirty plus years ago I proved that and engine that does not advance timing or change fuel delivery also runs more efficiently on higher octane versus lower octane fuels. As Doctor Fauci says, "It's just common sense". ;)

@kschachn So do I understand correctly that you are the camp that a motor designed to run on 87 does no better on 93? With over a million miles on those 4 cars, have you run long term tests on any of them? I'm with you, seat of the pants feelings can be and often are deceiving. It is also...

This is true as well but I also have driven cars that were not smart, the timing didn't change but they ran cooler, smoother and got better gas mileage too, back in the carburetor and early fuel injection days.

Sure Don! Haven't used a drop of ethanol this year so far. For anyone following, my trucks are fed a steady diet of 93 octane fuel or ethanol, never anything less than 93 unless by accident.

Excepting the newer DI engines, I have not driven a car in near 40 years where I didn't get better gas mileage using high octane fuel versus low octane fuel. Now, it may not always make financial sense but the cars did perform better on higher octane fuel. There's a difference in economy even...

Nope. Would be nice but once the incentives went away, GM quit making them FlexFuel capable.