We just purchased this Suburban.
Specs;
LTZ model
4.10 gear ratio (according to specs) 6.0L engine
124k miles.

No known or noticeable mechanical issues, except for some minor cosmetic items. We took it for our first trip and it Runs and starts fine.
Previous owner (original) said he had just changed oil, seems like new oil. He said all maintenance done.
Suburban is in great/excellent shape. We fell in love with it. It's got ALL the bells and whistles, but on a 600 miles hwy trip we're averaging 8MPG!
We know it's a tank, not expecting 20 mpgs, but 8?!
Is this really average with these specs?

What do you think? I'm hoping there's something wrong that I can fix.
Please give me some advice.
Thanks for reading!

 

Before I can tell you to check the compression on all 8 cylinders...

1500 or 2500 Burb?
Stock 4x4 LTZ all around, no big tires, no reprogrammed ecu?
Freeway at 80mph or 60mph two lane?

I've been getting great gas mileage lately, must be summer gas. Doing 55-60mph driving has been yielding 20MPG easily. Going 80mph out to Cali last January got me 15.5MPG in my 2008 4x4 LTZ 5.3 liter.

 

How are you calculating fuel efficiency? If you're using the onboard DIC, have you reset all meters, i.e. trip, fuel usage, etc. since you purchased the truck? Could be the PO did a lot of towing or just had a lead foot and those were his numbers.

FYI…I get better numbers than that (9-11 mpg) when I tow my 5700 lbs boat with our '08 burb, 3.73 ratio, 5.3L

 

Thanks for the replies.
Sorry, yes, completely stock, 2wd.
2 lane Hwy, average speed was 75-80. I will admit I have a lead foot, my wife usually gets better mpg than I do, but it's usually just a couple miles difference. She didn't do any driving this time.

This 200 mile drive in my Previous 2001—2003 Suburbans usually used up half a tank, sometimes hauling a flatbed trailer with a 2k lbs sand toy.

Trip computer and my own calculations are giving me this average. Not to mention I had an empty tank to refill at my destination there and back. I was hoping it was just bad gas at my fill up at home, doesn't appear to be the case, after 4 fill ups.
8mpg was Highway, I haven't even dared do the city average, but I've only had it for 5 days, most of our drive has been Hwy, so far.
Although it will be my 10 mile round trip commuter vehicle.

 

There has to be a fuel leak somewhere, or else you'd see a crap load of smoke coming out of the engine.

My 2008 4X4 2500 Suburban gets 15 on the highway, 13 around town, and I get around 8 when I'm pulling my 6500-lb trailer.

Something is seriously wrong. Do you smell gas under the hood? Maybe a fuel rail is leaking. Get the truck checked out asap.

 

A fuel leak also came to mind, but as much fuel as its using up, I would've definitely have smelled it. But I will still check.
It runs so well, it's got me stumped.

 

did you unhitch the 60' Searay?

8mpg is half of what I get and I'm stop and go, frequent passer (have to be over here).