Hey y’all from southern Virginia

Wildblue19

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I noticed when driving my Suburban at higher elevations (I-70 west of Denver in particular) the mileage was a LOT better. I guessed it was because of reduced wind drag... figuring drag is proportional to density, and the air at 5000-7000 is less dense than that at sea level.

At low elevations it used to get 17-17.5 mpg in factory trim (3.42 gears, oe wheels and tires). Now, with different tires (taller, wider, more aggressive tread) and a few other changes (3.73 gears), I'm in the 15 mpg territory.

It's a 1998 L31 4L60E.
Up in Colorado and Utah I would consistently get 16-18 mpg on my 93 burb tbi, stock everything. Now in Texas around 800 MSL best I see is 14-15 highway, town is more like 12-13. 3.42 gears 5.7. engine starting to get tired but thin air is a significant contributor.
 

South VA

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I noticed when driving my Suburban at higher elevations (I-70 west of Denver in particular) the mileage was a LOT better. I guessed it was because of reduced wind drag... figuring drag is proportional to density, and the air at 5000-7000 is less dense than that at sea level.

At low elevations it used to get 17-17.5 mpg in factory trim (3.42 gears, oe wheels and tires). Now, with different tires (taller, wider, more aggressive tread) and a few other changes (3.73 gears), I'm in the 15 mpg territory.

It's a 1998 L31 4L60E.
Hadn't thought of the air density, but in theory it makes sense.

Back in VA with the 2500 now, and I averaged around 13.4 mpg on the trip from Tucson. Most of the way I didn't go over 70, and had the tires inflated to 34 front and 46 rear. The recommended pressures are 50 and 80 (!), but the tires were old and I didn't want to push my luck.

It's in the shop getting new tires, a tune, and checking out the idler and pitman arms. I'll be interested to see if the mileage changes as a result the tune. I'll also try running it at the recommended tire pressures since I'll have tires that will handle it (Mich LTX AT/2), and see how the ride is.
 

Caman96

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I average mid to high 15’s with mostly highway some around town driving on 265/75/16 from 245’s. ECM is calibrated from BlackBear.
 
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