My post may be a little confusing. "Just as advertised" I meant the 14 mpg city driving, not the fuel grade.

Yes gm recommends 87 minimum in the H3, however GM highly recommends using "Top tier" gasoline. Switching to top tier, in the long run, will get you better mpg overall. Cleaner burning fuel, prevents carbon deposits, keeps the engine performance optimal=better fuel economy.

Here's a site that explains the fuel recommended by GM plus other automakers:

Top Tier Gasoline

Thanks. Sorry about that. I just don't know though in the long run if it really is a cost effective means, or if the benefits are of any major significance to use premium as your main fuel. It's something I've done some reading on in the past, but I really don't know what the answer is.

Because I know the amount of carbon buildup cheap fuel can cause on an engine, I always use premium, usually around 20c more a gallon. I always recommend to my customers, at least run 1 tank full of premium, for every 5 fillups. However it doesn't really matter what grade you use, if you get your fuel from a top tier supplier as stated on the site:

TOP TIER Detergent Gasoline Retailers

Gasoline retailers must meet the high TOP TIER standards with all grades of gasoline to be approved by the automakers as providing TOP TIER Detergent Gasoline.

In addition, all gasoline outlets carrying the brand of the approved retailer must meet the TOP TIER standards.

Additional gasoline retailers are added to the TOP TIER list as they meet the standards. The retailers known to be on the TOP TIER list are shown below.

Top Tier Gasoline

Ok. Yes. I usually use Shell to fill up. sometimes costco if im in that end of the city. I'm thinking about just sticking to Shell Regular Gas and filling up a tank of premium around every 5 fill ups like you say

That fuel does a hummer good (same so with any vehicle)! I also use Shell, only available top tier fuel around me.. Some people "eat healthy", ....... My H3 "drinks healthy"! ;)

Ya there is a shell right by where I live. So i'll start just using shell regular for a while. I'll see if there are any mpg changes

15mpg,no mods

2008 Alpha
 

I have been around Hummers since they came out...and finally purchased one two months ago. Mine is a 2008 alpha running 285/75/16's. All stock... Ran a can of "Sea foam" through the system on the first tank, nothing else. My mileage has been running around 16 mpg in town and 19 on the highway. Was pretty amazed with the MPG and wondered how it did it. Looked for add ons from the previous owner..Super Chip, exhaust, whatever and nothing. Totally stock out of the factory. The only thing I can think of is driving with a light foot and not driving it like my "71" Chevelle. Beats me??

Installed a cold air intake and throttle body spacer and have noted a pretty good increase in gas mileage. Went from ~16mpg to ~19-20 which is pretty good as far as I am concerned. Now to get a re-flashed PCM and a good exhaust system and I will be good to go :D

Running premium when regular is recommended does not hurt the engine, only your wallet. You get no more mpg out of it since regular and premium contain the same amount of BTU's. Premium has additives that make the fuel better resistant against self detonation (pinging). That is mostly required for engines that run a higher compression.
If you have an engine that requires premium and you use regular. Two things will happen. Mileage gets worse and you lose power. The engine will adjust its timing, causing you to loose power (and to compensate you give it more gas, hence the worse mileage.)