Hey. I really need your help. I am trying to help my cousin work things out his problem on 2005 Alvance Chevy truck. Its 5.3 liter only 85k mileage on it. Somehow he told me when he drive as roll from 0-55 mph start vabration. I told him let gas pedal off it was smooth. When you push the pedal its vabration. Then shift to Netural rev up some it was smooth. So drive its still vabration till about 60 or 65 mph it stop vabration. It could be missfire some spark plug. They never changed since they bought brand new ha.