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8.1L Gas Mileage

What is your average gas mileage with a 8.1L?  

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Hey ptmeyer84 - I get between 11 and 12 average with a daily commute of 30 miles (40/60 city/hwy). I've got 4:10s and 265/75s. On pure highway trips, I get close to 13.5 - not too bad at all. I just put on a TrueFlow air intake and didn't notice an increase in my daily average - probably because I get on it a little more now :confused: BUT I just got back from a 550 mile rnd trip camping trip down into the Navajo Nation in AZ with a 2500lb slide-in camper & got 11.5mpg !!! I normally got 8-9 with the camper. BTW - I live at 7000ft.


Take it easy & welcome :crazy:

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Good poll.


I'm driving 04 CC 2500HD with Big Block / Allison combo. Have 3.73 gears and 285 REVO's. Started off in the 8.5-9 MPG range around town and 10-11 MPG highway.


Changed intake to Volant cold air system. Got Westers tune and asked him to change spedo for tires and give me good MPG. Now I'm avaraging around 11-11.5 MPG city. And getting 13-14 MPG Highway.


Only complaint I have is my engine has developed the cold start knock. Aside from that I'm very pleased with the Big Block. Loads of power and pretty darn good MPG for a 496 cid engine!

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12.02 mpg average since new (hand calculated not DIC, DIC reads high), 95% rural, no city, 5% highway. High Altitude.

Bone Stock 8.1L 4x4 with 4.10's


If I reset the DIC while on the highway and set the cruise at 65 mph I can break 14 mpg. :rant:



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4.10's are an option and I have them. Also, 295/75R16 tires, 4" lift and I get between 9-10 in town. Towing the 5'er, 6-7mpg.




4" Lift and 295s I would have thought your 5er rear bumper would be draggin' on the ground :rant: Nice scenery in the background (PICTURE)




2001, 3500, 285s, 4.10 I get a tiny bit better than 11mpg on the highway.

7mpg towing my 11,400 fifth wheel.

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2006 2500HD with the 4.10s. regular cab and 4x4.

Got the six speed ally with it, awesome! Double overdrive gear is nice with the big block.

I am not much in a hurry when travelling out on the turnpike..generally do 65-70 mph. I dont have the steering control buttons so i dont know the instant fuel mileage but after a fill up, i generally average 11.5-11.9 mpg. I dont tow. Truck just turned 2500 miles.

Everything is stock.

I did have to replace a tail light because it burnt out and that was about 200 miles ago.



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11-12 mpg empty

10-11 mpg loaded


4:10's Allison, crew cab, long box, 3500SRW



My old truck....1999 GMC 2500LD 6.0, 4:10's, extended cab, long box


15 mpg empty

6-7 mpg loaded



Since my truck most often is towing or hauling a load it actually makes economic sense to own the bigger engine. My yearly average mpg is better with the 8.1 then when I had the 6.0

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Post your truck's model, gearing, performance upgrades and relative city/highway percentage.  I would like to see just how much worse the gas mileage is compared to a 6.0L.  Thanks





2003 ECSB 4x4 Allison trany

whipple supercharger @6psi

Dmax intercooler

4.10 rear / G80


I have no idea what i get for gas milage and i love it. Its gotta be single digits because i find my shoe getting stuck to the floor with the gas pedal underneath it everytime i go out on the road. Its like my foot is made out of lead or something...LOL

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I get between 10 and 11 average around the area I live, 12 to 13 Hwy and 8 to 9 towing my 10k lbs 5er. I've got 3:73s and 265/75s on my 2001.







How fast do you drive pulling your 5er? My 5er is about the same size and our trucks are basically the same, except I have an extended cab and 4.10's in it. I usually pull at about 65mph with the tow mode on and never get higher than 8mpg towing. Of course where I tow there are hills and I usually have to fight the wind too.

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I have a 03 3500 crew cab with duals. Before the wait 4 me I got 5-6 pulling 9-10 empty, after 8-9 pulling and 12-13 empty. I have a 28' fifth wheel weighing around 12000. I run anywhere from 65-80. LOVE that tune.

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