about a year ago i purchased a 06 Silverado 1500 5.3L v8. The vehicle advertises up to 20mpg in the hwy. I wasn't expecting to get the 20 in the hwy so I was ok when i was getting the 17mpg on the hwy. However, in the past couple months i have been getting a consistance 14mpg on the hwy and in town. Can anybody give me some advise on how to fix that? I like in a rural area where gas is $4 and up and have to drive a minimum of 250/wk and make a 900mile round trip across texas about 4 times a year. i would really like to get my milage up. I appreciate any input.