i have an 03 1500 4x4 sb with the hemi, and a K&N intake, throttle body spacer, magnaflow catback, and a superchip programmer on the 87 octane setting,and im pretty sure i have3.73s.the truck has a leveling kit with 35s also. im getting less than 15 mpg going 65, and about 8 or 9 in the city, even with these bolt ons. i want to add headers and a new y pipe, and wanted to see what kinds of results people who have added headers have gotten. how much if any, increase in mpg, and also was there a noticeable difference in power? any other suggestions to help me out? also, someone told me if i remove the front drive shaft i could save a little gas also since it still turns even when not in 4 wheel drive. any truth to this? thanks

 

well i dont think you have 3.73's bc i don't think they came in 1500's I could be wrong but i dont think so... The throttle body spacer was a waste of money and aluminum. The headers make a slight differnence in the low end torque and possibly a slight mpg increase with the better flow... also i would run the superchips on the performance setting.... works better for most of us... also are you hand calculating or going by the overhead also did you tune your truck for your tires?

 

I do have the truck tuned for the tires, and i have been calculating my overall gas mileage after filling up and average a little under 12 overall, but when im on the highway it shows about 14.7 using the overhead computer going about 65. what are you getting? the only reason i havent put the programmer on performance is because i will have to use 93 octane and didnt think my fuel savings would be worth paying the extra at the pump.

 

TD is right [:@], you don't have 3.73 gears, you either have 3.55's or 3.92's. If it's the 3.55's this would be your entire problem, they are robbing you out of tons of performance AND fuel economy. 3.92 still are not a good choice with 35" tires, but wouldn't be the huge drain that 3.55's would be. 4.56's would give you GREAT performance, at least the same fuel economy on the highway, and better MPG's around town.
First things first. The Superchips set for "Performance" and the use of 91+ octane fuel will see you enough MPG gains over the "87 Economy" setting to fully justify the extra 20 cents a gallon. That right there should give you a couple mpg's over what you are seeing now.
Headers would also fit in well with a cat-back exhaust and a CAI. Don't waste your time or money on anything less than Long Tubes though, the gains would not outweigh the cost. I picked up the most MPG's after tying in my Pacesetter Long Tubes. I don't think they give you much gains by themselves, but they really help bring the other mods together. I did lose a little low end torque from them, as I have next to no backpressure with them (enough that I welded the cats back on for the restriction and back pressure to get some of that torque back) but the mid and high end HP gains along with the better fuel economyare dramatic.