I got a 99 Two DR Tahoe 4WD with the 5.7 Vortec. Mods are ported TB, KnN,True duals with sweet thunder mufflers. My gas mileage is really bad. Is there any way to improve my mileage? Ive thought about swapping in a 5.3 or a 6.0 in hopes for better gas mileage. I would like between 14-15 city. Any suggestions? Thanks in advance.

 

What are you seeing now?

To me looks like 12-14MPG will be average for your kind of truck, seeing that a 4WD and all.

Check your cats to begin with see if those aint clogged.

 

cats are gone

 

I get 15 MPG all day long no matter speed with my vortec 350. Could be your injectors maybe.

 

Man, you could buy a ton of gas for what it would cost to swap in an LS motor. Use lightweight wheels, smallish tires aired up real good and keep your foot out of those pipes.