I am looking for suggestions/advice as to how to improve the fuel mileage of my old Ram 3500. I love my ol' truck, a '99 Ram 3500 24v 4x4 AT with no mods. The mileage is killing me. I was hoping that I could get some advice as to reasonable mods I can do to improve this consumption rate. We have one of the best Dodge Cummins high-performance techs in the country here in Lawrence and I know of his mods getting 1.5-2.5 times the hp and 25+ mpg, but I can't afford him. So any help will be GREATLY appreciated.

 

Did your mileage just start falling off or has it stayed the same over the years. In my truck with a simple intake, exhaust, and chip package i was getting 22.5 mpg. Then the mileage fell off consistently to 15 mpg. Turns out the VP44 was worn out and when i replaced it the fuel mileage returned. Just a thought read my sig for mods.

 

Cold weather creates a tremendous amount of drag in the axles, synthetic oil makes a huge difference. The transmission and xfr case already have a synthetic oil in them but you can also change the engine over to synthetic along with the power steering. A removable winter front will help with engine warm up even in spring and fall. A clean air filter along with a clean IAT and MAP sensors will also help. Low tire pressure also robs fuel mileage plus any extra weight the truck is carrying. The easiest way to improve mileage is to back off on the accelerator pedal. The AC compressor runs in the defrost position so if you don't need it select a floor position or turn it off and the compressor won't run.
There is probably nothing new in what I've said and if there was a magic bolt on device that increased fuel economy the gas companies would have bought it up long ago.

 

When I first bought the truck it gave me 12.5 mpg empty, city/highway. Appalled, I bought a jusg of PowerService and ran it at the mixing ratio advised. After 2 tanks of the mixture I got to 16, and then to 18 mpg empty mixed driving conditions. I have no idea what the reason was but it was a cheap fix.
The best mileage my truck had was right after the VP-44 replacement. It may be that your VP is old and not very efficient anymore.
I have no intake or exhaust mods and get the same mileage as others with those mods so my assessment is, those are not necessary for fuel economy.