My step-son has a 1999 Z71 ext. cab. He bought the truck used. When he got the truck it got 15+ mpg. He travels approx. 50 miles one way on an interstate to work. His mpg dropped to around 13 after a couple of years. After 200,000 miles he got a very low mileage engine from a 2004 Z71 and replaced his old engine. After his swap he still gets 13 mpg. What kind of mpg is everyone else getting and what can be done to improve his mpg.
Thanks

 

i can get anywhere from 19-21 on the highway driving with sense and using cruise control. I get about 14-15 in town.

running stock tire size? what gear ratio? you might already have, but start with the basics, clean/check air filter, check tire pressures, put some fuel injector cleaner in.

 

Do you have oxygenated winter gas where you live, it will affect your mileage aobut 1-2 mpg.