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  1. #11


    Yeah if your planning on keeping the truck I'd say 4:10 gears is a must. Also does your truck have the manual shifter option on the shift lever? If so let those rpms climb up a little before you shift and give you better power.

    2006 Duramax LBZ
    Edge Evo
    4'' Diamond eye to 6'' tip
    16'' ion alloy, 33'' fierce attitudes
    Lots of work left to do!

  2. #12

    Join Date
    Jun 2006
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.


    Wow- what does a Backhoe weigh-14,000 lbs???
    Except to hit maybe 2200 rpms at 70 mph-you can't beat the OEM engineers setup.CAI HEADERS EXHAUST- waste of $$ for F
    I'm surprised it doesn't downshift.You must be turning maybe 1850 at 70 mph in 6th?

    If those tire are pretty aggressive-lugged making plenty of road noise-all that noise takes fuel-the low pressure also takes fuel.
    Still 5 mpg??? When someone towing maybe 16000 lbs gets 4 mpg??You are towing maybe 3500 lbs?
    You have a 40 gallon tank?? Under 200 mile range?
    1998 suburban-
    1/2 ton

    199500 miles

  3. #13

    Join Date
    Feb 2008
    Red Wing, Minnesota, United States


    the C rated tires DO NOT seem to be right for a 2500 truck, they should be E loads, those tires could be part of the problam, as they are gonna flex more under load that will give you a bigger footprint on the road, creating more resisitence, but still shouldnt be enough to put you at 13mpg on the highway. Also does your truck have a tow/haul selector if so use it. Also i would not even allow the truck to run in 6th gear(if possible) if you can lock it out or manually select to be in 5th or even 4th i would do it. its probably causing the tranny to hunt for gears too much and chewing at your mpg.

    I wouldnt invest in getting the bigger gears, they are only gonna increase your rpms, and the stock ones are just fine.
    Last edited by vncj96; 12-16-2011 at 09:10 AM.
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual

  4. #14


    The 3:73 gears in the newer trucks are useless. Look at your tranny ratios and you will see both 5th and 6th are overdrives. With 265's I am just over 2000 rpms at 70 and I get 15-17 at this speed depending on which way the wind blows with a 2008 3500 crew 4x4 srw with 4:10s. I also have a 28ft heavy duty all sports steel enclosed trailer i put 6 sleds in and haul 1300 miles out west and my trip average is always between 8-9 mpg with that trailer my 7.5' wide 27 ft snow trailer I get over 10 when towing if I keep it at 70. 9.5 at 75mph. I have a guy I work with who says that his 2008 2500 crew with 3:73 gears will "hunt" and down shift just going down the highway. He has 245 tires and we live in lower Michigan. We barely have what anyone would call hills!

    As far as lugging goes, my 2008 doesn't have the grunt that the 6.0 in my 2002 motorhome has. However with 6 speeds and an engine that is happy running at high rpms it pulls better than any gasser I have had in the past and does it in a civilized manner...

  5. #15


    I have an '03 burb 2500 with 6.0, 3.73 gears and 285/75-r16 load range D tires. The tires being bigger have more load capacity at 3305 lb single vs stock tires at 3045 lb. It also has the 4 speed trans but with a 2000 rpm stall converter. The 6 speed gear ratio is better : 1st, 3.08; 2nd, 2.81; 3rd 1.41; 4th 1.0; 5th .76; 6th .67. The 4 speed is as follows 1st 2.48; 2nd 1.48; 3rd 1.0; 4th .75. I tow a 5500 lb camper at 60 mph in 3rd on the highway. OD is too high with the 285/75 tires. Just towed a trailer loaded with wood (est. 2500 lb trailer, 4000lb wood) and it was all in the Pennsylvania country. I only used 3rd gear. Going to stock size tires next time. The tall 1st gear makes it hard to start off and the rest of the gears are too far apart for making towing efficient.
    2003 Suburban 2500 LT, 6.0l Volant cai. 3.73 gear. Mobil 1 syn oil

  6. #16


    i had most of 6000lbs behind my truck with a flat front 6x12 uhaul. i still managed 11 ish on a 13 mile trip. with hills.

    same truck and info as in sig.

    i wonder if its a fluid issue. my old neighbor had a 01 2500 with the 6.0. got like 7 mpg empty or loaded. turned out that some idiot had put 80-90 gear lube in the rear end instead of the standard gm stuff, swapped the fluid out and he picked up 3 mpg.


    2011 GMC Sierra SLE 5.3 Z71 4X4 Stealth Gray Metallic / 2004 Chevy Impala LS 3.8 Cappuccino

    Tow mirrors - Diablew Tuned - Flowmaster Regular 40 - Ready Lift 2.5' lift - BFG LT A/T K/Os - Carr Light Wing - TruckLite LED lights - Optima Red Top - 50% Front Window Tint - Line-X bedliner - Airaid MIT - Tekonsha P2 - ARS Billet Grill - Fia custom fit seat covers

  7. #17


    My 2000 6.0 is running 11mpg empty with 285/75/16 and 3.73 gears id expect a little more, might be the wear? 280,000 miles and some change? towing 10,000# it gets 9 id expect a little better empty like 13 i drive 80% highway or country road

    2000 Chevy Silverado 2500 4x4

    6.0L v8:great: 4L80E

    2.5 in Daystar leveling keys

    285/75/16s BFG ATs on HD wheels

    Cab lights and tool box

  8. #18


    I get 10-11 empty, all short trips on mostly back roads with lots of hills. Can squeeze out 13-14 highway. Towing 5000lb camper is 8-9 mpg. I have a 2000 rpm stall converter that hurts the milage.

  9. #19


    Quote Originally Posted by hunter541 View Post
    well like i said its a 2009 2500 6.0 3.73 gears, it only has 27,000 miles on it so its hardly broke in,it has 2657516 tires they are a little agressive there only c rated so the low pressure lights on for the rear,planning some e rated 2857516 in the seems it does need 4:11 rear,hell at 65 mph in 6 gear its only running 1700 rpm so its just like my 1500 that thing at 80 mph was running around 2000 rpm,six gear seems worthless when towing because of the rpm range i think the guys with the 4 speed old 6.0 with a 4:11 rear was a great towing gear,i think towing around 2200rpm is about perfect i guess i need to learn how to drive agian do you guys think that any programmers would help they say the stock exhaust is really good that any headers etc wouldnt help much any imput so far would be great thanks agian

    Your 265 tires will cause the 3.73 gears to act like 3.60 gears, not helping. I Just drove to Texas from PA in my '03 burb 2500, 6.0l, 3.73 gear, 285/75r16 D range tires. Got 14mpg at around 65. Noticed any thing over 2000 rpm made mpg drop up to 3-4. Not worth it in my opinion. 55-60 mph seems best with these engines.

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