i own a 2006 z71 crew cab and was constantly getting 17.8 mpg until one day it just dropped to 14.4 on the highway. engine runs fine. used fuel system cleaner, air filter, mass air flow cleaner. nothing works. what happened ?

 

fuel regulator? is tranny runing fine?

 

Try changing fuel filter?

 

How many miles are on it?

 

149000 miles. tranny is fine. have not changed the fuel strainer since it is a pain in the butt to pull the bed off that truck to get to the fuel tank but I may have to. I was trying everything else before I did that.

 

Spark plugs and wires? Clean the throttle body? Run some seafoam through it to see if anything is clogged up

 

All the comments recommended are fine, but won't change anything if the fuel you have in the tank has a higher % of ethynol. The more there is, the worse your mileage will be.

 

I do have a few questions, has the mpg been bad all winter? Been fillin up at the same place(s)? Did you increase tire size or have low pressure in your tires?

 

I usually fill up at the same station. Tire pressure is 35 psi. I changed plugs 40k ago. I changed tires at 20k ago. It pretty much started when I changed out an evaporator solenoid canister. GM does not make a replacement part but they offer a replacement kit that is different and $160. I ordered an exact canister off the internet for $15. Check engine light went off but gas mileage dropped.

 

Try putting in the old canister (if you still have it) or a junkyard canister and see if mileage improves.