improving gas mileage on surburban 98

I have a 98 suburban with the 5.7 liter engine. Driving a careful 55 mph gives me 21-22 mpg on the level in Iowa, On hills and winding roads drops down to 19-21 mpg. Driving freeway speeds with the air running and keeping
up with traffic going 75 mph drops me down to 17-19 mpg.
I am interested in knowing if I can do anything under the hood to improve mileage, Ive seen electric fans, synthetic oils for the gear boxes yet I do not want to venture into this area because I suspect I may be wasting money by getting 0.00001 mpg improvements, but then, I dont really know.
Also, can I do anything with aerodynamics to reduce drag....fold back mirrors (maybe this is extreme) for example, airflow deflectors..etc???
How about the daylight running lights, anyone know what shutting these down will do?
Any ideas?
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Consider your self lucky your getting that good of mileage. Thats good mpg inho.
my 92 blazer with the 350 gets 16 on a good day. and Its half the size of your suburban.
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Our 99 Jimmy gets 15-16 on the highway if were lucky and all we got is the 4.3L.....Dont even wanna discuss what it gets in town.....that explains why its been sitting for almost a month now.

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Something is wrong with that 99 then. My old 94 with 4.3 gets 18 around town and closer to 21 on the highway. The 2002 we just picked up got 22.4 on the road last weekend (534 mile RT to Cabelas in PA.).
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Steve W.

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What he said, my 98 gets 21-22 on the highway (75 MPH) and 17 MPG in rush hour traffic, lots of accelerating from a stop, then stand on the brakes, repeat often. One of my O2 sensors failed, as defined by a code, with a noticeable drop in mileage for the two weeks until I could replace all of them. Dirty air filter will also make a big difference.
Steve W. wrote:

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"mudmonkey" wrote:

Yes lucky indeed, do not touch a thing except maybe tire pressure. I have a 89 4x4 burb that will do about 19 mpg at 65 mpg on a trip from Ohio to South Carolina on one tank of fuel (565 miles on 30 gallons of gas and it holds 40 and A/C was on too) Never checked it on long a pure flat land test in recent times. It has stock sized smooth tires with 3.73 gears, a large single exhaust with a flow master (3 inch exhaust and it is quiet in car) and it has 175k miles on it too. I also use premium fuel in it year round (occaisionally 89 in winter but it is rarely drive in winter) and the timing is set 8 BTDC as the baseline. It never ran as well or delivered much over 15 MPG when it ran on 87. Runs like a champ in current setup. I have had it since new and plan to keep it at least till kids are done with college in another 6 or 7 years.
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buy a different car. That's pretty damn good mileage for what you have there.
DRLs might cost you .0001 MPG. That's the least of your trouble!
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Per hardworking:

On a good trip, I get 14.7 highway.
Once I got 16....
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"user" wrote:

Try a couple tanks of higher octane gas and you may be surprised.
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Sno Man, I don't think the premium will help here, the pre programmed timing curve is controlled by the pcm and is not calculated for anything other than 87 octane , it cannot without reprogramming, advance the timing sufficiently to take advantage of a higher octane fuel.

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Just an FYI - thats about the same I get on my Avalanche. No one ever believes me.
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Your getting great mpg! Try getting 12 city and 14 highway.
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