New here, I drive a 2005 3.5L Colorado Z85 and i average around 15 mpg. Is this average or do i have something wrong? My oil gets changed every 3,000 miles and there are no check engine lights on. Also when sitting at a stoplight, i can feel a slight vibration, also my drivers side mear slightly vibrates going down the road, but my passenger mirror does not. Is this because of uneven tire wear? Or could something else be wrong? Maybe a misfire? I know thats alot to ask of a first post, but i am a slightly concerned owner who doesnt have a vast knowledge of trucks.