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6.0 mileage issue

Is he sure it’s in overdrive. My 6.0 3500 dually with service bed and extra boxes on top of the service bed gets 9.6 mpg and it’s LOADED with tools and HVAC parts.

The 6.0 2500 HD work truck before this without a service bed got 11 mpg.
 
I always averaged 13 to 14 with my 2000 6.0 on highway. But that was with 3.73 gears. If his is 4.10 then 10 isn't a stretch
 
My 2001 suburban k2500 got 16 city hiway combined when empty. Loaded with a complete 6.5 engine in the back with another 500# of hoist and tools, roof rack full of about 700# of crap catching air. 850# worth of people. Got 16.5 iirc mpg on the hiway.

When people and cargo was maybe 1100# and towing our little single axle camp trailer, I drove like a cop was behind me and got 14 mph hiway usually.

BF Goodrich a/t, some REVOs, and the BigO tires version all basically same tread pattern. No clue what gears.

Keep in mind my wife always leaves the red lights at the front of the pack, and 85mph on the freeway. Me on the other hand- I make fun of her driving it slow like a grandma. When the red light goes off: pedal down and if you even see the light turn green you might loose so as hard as you can without spinning tires. Sold at 205,000 miles.

The recently totalled 05 Escalade with 6.0 full time 4wd 1500:
Got 13.5 mpg was the last numbers from it but that was mostly city driving that tank with me behind the wheel and on the gas too much. Yes, too much 1 time for sure! Haha. On its way to the auction yard with 127,000 miles iirc.

We both agreed to drive her new to us 07 tj cruiser nice and easy, and never more than 5 over on hiway. Kinda have to now with “crash year 18”. Haha

I would say do an in tank injector cleaning additive and the upper intake cleaning that is done through a vacuum hose.
A lot of people go really easy on the 6.0 and it carbons up. Blow that crap out and she is much happier. Kinda like the newer diesels that get plugged up egr and turbo from grandma putting to the grocery store.

How many miles? Mi
 
X-2 on the question about the rear. Higher than 4.10's?

And, just gotta ask . . . Up to date on the plugs and other ignition related items? Reason for the question is that I had a bike with an 8K mile plug replacement cycle. Did not notice that in the maintenance schedule and wondered why mileage was down and it seemed a little sluggish. Had it in the shop at ~10K miles for some reason, they replaced the plugs, and it was zippy again after that. Also, have noticed in friend's gassers of various brands that neglected wires will zap power.
 
So more info at 2000 rpm he's indicating 64 mph. I'd think that would make it 3:73. His towing weight was around 10k. He bought the truck with 15k on it and it's been this way the whole time he's had it. Runs good pulls good just gets crappy mileage
 
Oh yeah- the computer calculator on both my suburban and Escalade was way off and read low on mpg and how soon you would run out of fuel.
 
You cannot compare an suv to a truck for mpg. Different ecm programming in them. Milage is completely dependant on the driver. My uncle had an 05, 3500 srw with a 6.0l. He never got better than 12 out of it the whole time he had it(430K miles), but the 1 time I drove it to Boston and back, I got 15.5 out of it. 9-10 is a bit low, but not outside of what others see out of them. I can't remember which cam 01 got, but I know there was some changes to the cam through the years that made quite a bit of difference as well as the tuning(01 ran pretty low timing compared to other years I've looked at). 01 was also the 1st year of the aluminum heads, so tuning was still pretty conservative there from the carried over tuning of 99-00 with cast iron heads. I'd say make sure the engine isin good tune(iridium plugs, 8 mm wires, clean throttle body, NO k&n air filter, clean maf), make sure the convertor is locking up good, but if it's been that way that long, then there's probably not much you can do for it.
 
not sure on the fuel calcs but I've seen the tires, pretty much a stock looking tire. Ferm would he benefit much from a different tune?
 
If all the maintenance items are up to date, the only other thing I would consider is to check on the version of tune in the computer. The '12 Burb I borrow on occasion went from 8 mpg towing my trailer to 10 mpg (on flat-lands) with just an update in GM's code (no aftermarket tune) on a completely stock truck. Mileage was hand calculated.

The actual reason why we updated GM's code was a periodic 2 - 3 shift flair when the weather and motor were cold. Tranny shop saw the computer version was a couple revisions out of date and pulled down the current one. Mileage improvement was a nice surprise.
 
It might help getting a tune, but some trucks just get bad milage. I would also make sure the thermostat is good and the engine is getting up to at least 180-185 actual temp(not guage, but actual on a scanner). Just a couple of degrees colder can keep it from going to stoich and leave it running in warm up mode.
 
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