i've got this posted on the general discssion forum as well. i have an 04 z71 with a 5.3, my previous truck was a 99 z71 with a 5.3 i ran 34/10.50-16lts on both trucks. both trucks are stock. the 99 had 275,000+ when i sold it. the 04 has 82,000. the difference? the 99 got 14.5 mpg. the 04 gets 10. some body help please.

 

Different tires? Low on air? Plugged up air filter? Leadfooted?

 

naw same tires, 45 lbs psi, new filter, no lead foot, that left in highschool.

 

Different axle gear ratios. The '99 may have had 4.10, newer truck may have 3.73 or 3.42 gears.

 

Beat me to it.

 

That was my guess too. The 4.10s are going to move those tires easier and get better city mileage.

 

nope, same diff set. i didn't know if there was any way that the ecu could go into like a default mode. i dont even know if thats possible.

 

Check O2 sensors. I would guess they are bad.

 

tunes are definately different, Timing maps are different, etc...

 

i would think that they were bad, but they dont seem to be. no rough idle, hard start or anything. maf sensor is fine aswell, i cant think of anything else...