Bad mileage with a 6.0l

[brandon684]

My 6.0l 3/4 ton, short cab, long bed, GMC is getting terrible mileage. It only gets 10.8 mpg in mixed driving. What can I do to improve the mileage?

[leolkfrm]

welcome to the forum
what year? what transmission and how had do you drive it?

[brandon684]

Sorry about that, 3/4 ton, automatic transmisson, 40,000 miles, 2003. I drive it really easy, trying to get better mileage, but it doesn't seem to matter. It just doesn't want to shift to 4th until 46 mph, and most of the roads I drive on are a 35 mph speed limit, so the fastest I will go is about 42, which seems to really kill the mileage. I was told by the tech guy at the dealership that the programmers will not allow you to lower the shift point, only raise it, but I don't know for sure, as they advertise that they will.

[Erock80]

Hmm... mostly when I see guys fussing about their mileage I usually say, "dude, get off the pedal". But in your case, all I can do is add a little insight.

I've got a chevy too, it's a 1/2ton, well not really, I made it a 3/4, but anyway, it's got the 5.7. Not exactly the same truck, but close enough. We'll say it's apples to apples, it's just red delicious to golden delicious. Nod if you're still with me. Anyway, my mileage SUCKS in town. That 30-45mph speed just sucks fuel for some reason. I get it out on the highway at 65 and I'll easily see 20mpg.

So, I'm guessing that big ol' V8 just wants to get up and gallop. In all honesty though, you should be getting better than 10 or 11. Try checking that no brakes are draging and that there's no wheel bearing problems or differential issues. Oh, and lastly, make sure it's not stuck in 4wd. That can happen with those push button deals.

Well, good luck.

Eric

[mudseeker]

your problem may be your convertor(not really anything wrong wth it). most of them are set to lock up over 45mph. you may have noticed your truck chugging around when your in that speed range, that's your convertor trying to lock up. stay away from that lock up zone and see if your mileage improves.

[wild bill]

welcome to the 6.0 club your getting about average with 4:10 gear's especially if 4x4

[brandon684]

What about the programmers, cold air intakes, exhaust? Is there a chip/programmer that will decrease the lock-up speed to 35 mph? (I'm guessing not, but might as well ask.)

[mudseeker]

a programmer may be able access the TCM and change the lock up setting, but i'm not positive on that.

[pscheers]

i have a 2003 silverado as well with the 6 liter 3/4 ton with the 4l80e tranny, and on the highway i get 16 mpg .. it took me 42 liters of fuel to travel 186 km ..lol.. hope these units of measurment dont mess u americans up ..lol ... no harm ment ..... i bought a super chip programer for my truck and it improved my milage a little .. i just bought some headers , and im planning on putting in the dynatrack free wheel kit , other wise known as lockin hubs , so there is less drag on the front end .. i was talking to a fellow at my gm dealership the other day , adn he was telling me that they are a pig on fuel , but u can pull a house off the foundation with it .. i hauled a double car trailer with 2 stock cars and equiptment , i never even knew it was there ... my friend put headers on his 6 liter , he has the exact same truck as u do , and improved his mileage quite a bit ..there is also a tranny shift kit u can buy to fix your torque converter issue , that chuggin is a new thing gm incorporated into the 4l80e and 60 e trannyies called torque manegment , it basically trys to limit the wear or strain put on the tranny when the motor is floored or kicked down .....

[pscheers]

here is a awsome message i got from stumppuller , he knows his stuff , i hope it helps ya , and im sure stump wont mind me sharing the info ...

Quote:
Originally Posted by pscheers
good day puller ...i was woundering if i could ask u a question , i have A 2003 chevy silverado , with the 6.0 liter. i was reading a thread where u metioned u installed a TRANSGO 4L80E-HD2 kit ... i have a 4l80e and my truck lugs alot , im haveing a tuff time in figurign it out ... i have some shortie headers im goin to install , and i want to do the custom tune u were telling that guy about in that thread ... could u fill me in on the shift kits and custom tunes , what would be the best kit for me to go with? thank i would appericate any help you can provide me with .. thanks aganin

Well there are three kits available with transgo, stage1,2,3, basically the stage 1 is towing and for R/Vs, stage 2 is street and strip (and comes with three different pressure settings) stage 3 is a full manual valve body and is for racing only. So i would recommend the stg 1 unless you intend to race your truck or artificially aspirate it. (thats why i got the HD2 and choose the highest pressure setting) Because i will be putting alot of HP to it with the supercharger.

As for custom tunes its unbeleivable the stuff they can do, your truck probly has touque management programmed into the trans, making for sluggishness off the line and during shifts, this can be adjusted or removed, they can tune for max power on any fuel you choose (reg,mid,or high grade) they can remove speed limiter, adjust for tire sizes or gear changes. any things that you add from stock like exhaust, CAI, can be tweaked to optimize its effectivness on the engine. Also if you choose to remove your catalytic converters they can tune the ECM to ignore signals from the rearmost O2s (I did this) so basically no CELs. They can also adjust your engine to run properly if you install a lower temp thermostat. I`ve even seen them be able to go into your cluster and put in custom words in there, that is too cool!

What i found with my custom tune, (and i tried a few) is that beleive it or not its cheaper to run the high grade fuel tune, I just got far better fuel economy on it, i was surprised, nice cause then i can have all that power all the time!

there are many tuning places out there, In my local area WESTERS is big here,(they are actually from alberta) and the local guy is great and i`ve actually gotten to be good friends with him. they have a website westersgarage.com they have listings in there, there could be one near you!
there is many others, nelson, wheatley, wait4me,blackbear are some of the bigger names, check and see which one is local online and go from there, if you have any more questions fire away, going to be out of the house today, and working outta town next week but i will have my laptop so i will try to get on...later...stump
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