I just bought this 2003 GMC 1500 HD crew cab short bed 4x4 to drive in Montana. I knew the gas mileage was going to be worst but I haven't seen over 10.5 and the power is less than my 06 5.3 Chevy ext. cab. it has a cold air intake, other than that it is all stock. I noticed the other day that the muffler was dented and had a mechanic tell me that it was from back firing. I have never heard of it doing that with three cats under it. the list of things I have run across my mind- tune, exhaust, cam, blower, headers, or gear ratio. would a cam do a big difference for power cause it is sluggish and slow for the amount of gas it uses. love the truck but it needs some help. on a budget also so I cant drop a $1,000 like it was nothing. I would like to add a supercharger in the next few years but I don't have the money yet. brands, specs, models, and price estimates are where I need to start. any help or info would be greatly appreciated please, and thank you for taking time to read.

 

start off slow and build it gradually. Don't jump in. What kind of miles does it have and what rear end ratio does it have? MPG won't be good in a HD but should be around 12 i'd think. Give it a tune up, clean the throttle body, check the mass air flow sensor and see if the honey comb is still on it as well, other usual stuff like filter,plugs,wires, fuel filter etc.

I'd start of with longtube headers, custom tune, and a new muffler dependin on what brand is on it.

 

The truck has 4:10 gears runs 10.5 mpg and idles rough in the cold. There is a mechanic shop that said they would tune it for me for 300. I am going true duels cherry bomb vortex. Idk about headers yet. 83,000 miles all stock except it has k&n cold air intake. Would the mechanic tuning it be better than black bear tuning do you think?

 

depends on if he knows what he's doing or not honestly. If he doesn't he could really screw somethin up.