'03 GMC 6 litre mods

Sleeper700 · Apr 17, 2009

The newer 3/4 tons have a much better transmission in them (6 speed). We had an 04, and it was horrible. I have a hard time convincing the owner of my company to try a new one out, but I keep telling him that it will be as good as the new 1/2 tons (they still only have a 4 speed).

Wise Mechanical · Apr 17, 2009

Im running a 99 GMC 2500 with the 6l I put a Westers tune in it and Air Raid, Edelbrock headers and a 3" flowmaster cat back, Im running 285 All Terrains. When not hooked to the trailer the truck rocks though when i have my deck and two quads on pulling a 24 ft holiday trailer the 4 speed just doesn't cut it, a 6 speed would make a world of difference!

hintonite · Apr 18, 2009

I have a 05 chev 6l motorhome and i am getting 16mpg pulling my 20' boat back and forth tothe coast. I am very suprised at the fel millage i am getting with this stock unit.

supermax · Jul 18, 2011

Reviving this old thread.....

Well, I still have this truck. Have new exhaust with hi-flow cats and a Magnaflow dual in and dual out muffler with 2-1/2" tail pipes..it sounds good.
Also have a Cortex tuner and throttle body spacer. Also and Air-Raid cold air intake. I tune it for towing and run 91 octane fuel.
This thing is still maxed out hauling my ATV's and trailer, two Rubicons on an STF deck with a couple hundreds pounds of gear and fuel under the deck and a 22 foot trailer that's 4700 lbs dry, so I'm thinking it's at least 5500 loaded with food, water and gear. Truck is driving me crazy. I gotta get some headers and something else to wake this thing up....don't want to drop the coin on a Duramax just yet.

Has 188K on it and runs great unloaded...what to do..?

medler · Jul 18, 2011

My K&N filter fell off this spring,,,oops guess i didnt tighten it enough....so i have no idea when it fell off but now i am worried how much chit got into the intake ,,but it is dirty in there...,,bought some new tires ,,,265's and the millage sucks again,,,, truck computer says like 16 mpg,,,wtf bigger tires cant make that much difference,,,and with the trailer on and the quad on the deck truck computer says 10 mpg...i have given up,,,just drive the SOB..

vanislerev · Jul 19, 2011

wouldnt worry about the duramax that much. i went from a 03 ZR2 sonoma with a 4.3 to a LMM duramax and got pretty much the same mileage 13-16. shitty. then dropped the duramax for a 02 sierra heavy half with the 6.0 and get 16-18. tell the truth i enjoy this truck more than the duramax... why i dont know

tex78 · Jul 22, 2011

the septer intake kits are like 200.00 for the hole kit.... put on on the wifes tahoe with a 5.3 2000... that and a power tower and she gets 24 mpg...

SLAYERMIKE · Jul 23, 2011

a cam can really wake those up too! :beer:

'03 GMC 6 litre mods

Sleeper700

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Wise Mechanical

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hintonite

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supermax

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medler

I love guns

vanislerev

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tex78

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SLAYERMIKE

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