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please check my math on mpg.

This is a discussion on please check my math on mpg. within the GM Trucks forums, part of the Vehicle Specific category; I just want to double check that I'm doing this right. I filled up my truck last friday with 19.7gallons. ...

  1. #1
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    sandstone grey
    2009 silverado

    please check my math on mpg.

    I just want to double check that I'm doing this right. I filled up my truck last friday with 19.7gallons. drove the truck mostly highway miles of 317.7 miles. I filled it up this morning and it took 19.4 gallons. now if I average the gallons at 19.5 divid that into the mile I get 16.29. is that right? am I really getting that shitty of a mpg even with dual exhuast and cai? I drive very safe and hardly ever stick my foot in to it. I am noticing that driving down the interstate at 75 mph. the rpms are right at 2000 and even if I push the trailer towing button theres no change. it has a 4l60e but does not feel like overdrive. wtf? trans temp on the interstate is 120 f. in town most I could get it was 130 f. any help would be appretiated. oh and it has the 5.3 and 275/ 55/ 20 tires.

  2. #2
    None Shall Pass Knight's Avatar
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    99 WS.6 - Modified

    Your math is correct.

  3. #3
    Your dealership guy konigandy6's Avatar
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    2008 Corvette Z06

    It's an 09 right? Do you not have a 6 speed auto trans? Also is it a Z71? 4x4? What axle ratio is it running. I'd hate to say it, but that is actually decent mixed traffic fuel economy for that truck.

  4. #4
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    sandstone grey
    2009 silverado

    trucks a 09 2wd 4l60e trans its a lt trim. boy if thats about average, they dupted me. I was under the inpression that highway stock was around 20-22. in town, yea I can see 16-18 stock. I figured with the cai closer to 22hwy 18in town. very dissapointing.

  5. #5
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    2007 Cadillac Escalade
    98 Camaro SS, 09 G8 GT

    Try lowering your highway speed to 65~70. You'll probably do 1~2 mpg better. You need to get yourself a tune my friend. I gained almost 2 mpg avg highway with a tune on my truck after supporting mods. Do you have a cover on the bed? Those 20's are heavy and will hurt you alittle bit. What's yout tire pressure? There are lots of little things you can do to get better mpg....the trick is to make your truck as efficent as possible.

  6. #6
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    sandstone grey
    2009 silverado

    definatly going to get a cover. the 20s are stock but I see what you mean. I guess I'm gonna have to bite the bullett and get a tune for it.

  7. #7
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    2007 Cadillac Escalade
    98 Camaro SS, 09 G8 GT

    Quote Originally Posted by chuck75 View Post
    definatly going to get a cover. the 20s are stock but I see what you mean. I guess I'm gonna have to bite the bullett and get a tune for it.
    You will NOT regret it. Believe me, I understand what your going through. When I had the 03' Yukon Denali and it was stock, I was lucky to get 16 mpg highway. After all the mods and making everything as efficent as possible (added E'Fans, 40 lbs in the tires, Tune, CAI, UDP, Corsa Catback, New plugs and wires, seafoamed engine, etc) I was getting consistent 20~22 mpg highway trips not to mention a nice gain in power. You'll get there my friend, just takes time.

  8. #8
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    sandstone grey
    2009 silverado

    thanks deezl. I went and bought a cover last night and my gibson should be here monday or tuesday. after that I am going to see if there is a tuner here in tampa the can do it. by the way whats a udp? a under dash tuner?

  9. #9
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    2007 Cadillac Escalade
    98 Camaro SS, 09 G8 GT

    UDP is under drive pulley. No problem, if you have any questions, feel free to hit me up.

  10. #10
    Your dealership guy konigandy6's Avatar
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    Tampa Tuning


    Check out these guys, they are a sponsor here.

  11. #11
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    sandstone grey
    2009 silverado

    Thanks, I shot them an email

  12. #12
    Impounded
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    gmcheviac

    I think I said in another thread that your rpm at that speed is normal. Switch to 17" wheels w/ 245/70 tires for mileage and add a soft tonneau cover. Tow/haul doesn't keep it out of o/d, just firms up shifts and holds gears longer. You already have electric fans.

  13. #13
    That guy thearborbarber's Avatar
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    White over Red
    1991 Suburban

    I get 20mpg when the cruise is set at 55mph on level ground with no wind. At 75mph I get 16mpg like you.

    2009 GMC Sierra 1500 5.3L 4L60E 3.73 rear 4x4

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    Senior Member Zboner's Avatar
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    Quote Originally Posted by thearborbarber View Post
    I get 20mpg when the cruise is set at 55mph on level ground with no wind. At 75mph I get 16mpg like you.

    2009 GMC Sierra 1500 5.3L 4L60E 3.73 rear 4x4

    I have the 4.8 and get the same shitty mileage

  15. #15
    Senior Member bluehawk2000's Avatar
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    midnight blue
    2000 trans am

    Yea lower your speed to 65 or 70 that will help, I do alot of hwy driving myself in the t/a and I don't hardly ever speed. And I have always heard that the covers over the bed doesn't do anything anyway, Cause I mean the bed has a pocket of air in it so the air does nothing but flow over it anyhow.

  16. #16
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    What are you guys whining about? Our Suburban gets 13.5 mpg on the highway... with a tailwind.

  17. #17
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    sandstone grey
    2009 silverado

    thanks for all the replies guys. I did put a soft top on it friday after work. I also got a call from Phil at Tampa Tuning and it looks like we're gonna get something going after I get the headers installed this weekend.
    Now I have a new question about the tuneing, I was told you have to run 93 octane fuel if you have a custom tune installed to keep from detonation. I didnt ask Phil about it when he call because I didnt find this out till this morning. anyone else have to run premium gas?

  18. #18
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    sandstone grey
    2009 silverado

    oh and one more question, is there a speed setting that the dod stops working? I notice it at crusing in town speeds but not at highway speeds?

  19. #19
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    Quote Originally Posted by chuck75 View Post
    Now I have a new question about the tuneing, I was told you have to run 93 octane fuel if you have a custom tune installed to keep from detonation. I didnt ask Phil about it when he call because I didnt find this out till this morning. anyone else have to run premium gas?
    The PCM generally has a low octane and high octane spark table that it utilizes. As long as the tuner does not copy and paste over the low octane table to remove it, I do not understand why you would be limted to premium fuel only.

    Quote Originally Posted by chuck75 View Post
    oh and one more question, is there a speed setting that the dod stops working? I notice it at crusing in town speeds but not at highway speeds?
    Our DOD works fine at highway speeds. Get it up to speed and then ease off on the throttle, or running on a downhill, and it should kick over to 4 cylinder mode.

  20. #20
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    sandstone grey
    2009 silverado

    ok I guess its just not as noticable at 75mph. I set my cruse at 75 on the interstate every day and didnt notice it.

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