skylar troutwine

Alright guys, hate to ask again but i am beyond confused, So i have been trying to increase fuel mileage in my truck for a bit, due to the fact that it gets 8-10mpg i feel like it should get a bit better (yes i know its a truck), and so far i have done almost everything people have mentioned, So far i have replaced catalytic converters, fuel filter, air filter, o2 sensors, spark plugs, injectors, pcv valve, cleaned egr valve, cleaned throttle body, seafoamed it, ran fuel cleanee, checked for dragging brakes, proper tire pressure, fresh fluids all the way around, cleaned maf sensor, and none of that helped gas mileage even one bit, so i went and got a custom tune the other day just to wake the truck up a little bit. And to my surprise, the tune didnt help not one bit, on the highway today, for 100 miles, i got 8mpg the whole way, and city i got around 9.5,( doesnt make sense) But my question is, after all that stuff, and even a custom tune i havent gained not even 1mpg. The motor runs and drives fine, no ticking, clean internals and everything, is there something im missing, i know its a truck but i feel like this gas mileage is a bit alarming considering whats been done to it And i drive it very easy 99 silverado 5.3 4x4

bammax

It's a 4wd so it's heavy. If it's crewcab or longbed then it's basically a tank. I'm guessing it also has a towing/offroad gear ratio which will be murder on highway mileage. If you need good mpg trade it for a 2wd regular cab shortbed with 3.07 gears and you'll get 20 mpg.

GMTECH4

I know a guy gets 18mpg hwy on a awd 4 door gmc truck with heavy 22' wheels and a 6.0l that my buddy tuned. what are your fuel trims.