Hello, I’ve got a 2008 GMC Sierra SLT with z71 package. I’ve had it stock until this year (2020). Recently put a level it in and had the truck aligned and it ran great. Went to put new tires and rims which are 33x12.5 Toyo open country AT2 extremes on 18x9 fuel assault wheels. The truck obviously had a decrease in power and mpg but recently it has gotten significantly worse.
On HWY I can get 18-16 but recently in the city I am getting 11mpg!!! I live in a city with a lot of hills and windy driving so I can attribute that to some of it but it seems low.
I’ve looked around and some guys suggest checking air sensors and tune ups, but I am wondering at what point is it a bigger issue? Or is it the reality of a lifted truck with heavy tires?
any suggestions are welcome, it has not been 11mpg for long just the last month. Thanks