I have a 96 1500 4x4 suburban and mine does 17 on highway, it used to do 14 on highway, what made it so efficient was the Fitch fuel catalyst fitchfuelcatalyst.com, and also the help of E3 spark plugs e3sparkplugs.com, which you could get the plugs athttp://www.partsamerica.com/productd...60&PTSet=A, but the fuel catalyst you could only get at http://store.summitracing.com/egnsea...115+4294908216

 

'06 Suburban LS 4x4 5.3L 29,000 miles
Regular gradefuel.....tires at 40 lbs...light foot on throttle.
City 14mpg
Highway 22mpg@ 65mph 20mpg@ 75mph

 

I just bought an 07 burb LTZ and getting about 16.5 to 17.5 on the highway. My 02 Yukon xl before this one was at 19. I am not very happy either.Doesa chip help with gas mileage?

 

I'm jealous! 06 Z71, 75,000mi, 20" wheels, 45lbs, Flowmaster exhaust, Drove to FLA from TN(70-80 MPH)and avg 14MPG. But as was posted earlier, I didn't buy it for the gas milage.