I have been searching this and other forums regarding the in town mileage on my 03 GMC 4WD 5.3. My first thought was pulling the engine and recamming, possibly a bump in compression, smaller valve and port heads if they exist and whatever else I could think of at the time to trap cylinder pressure in the lower rpm range. I haven't found anyone yet that has tried a strictly mileage build on one of these and it just occurred to me that maybe I am trying to use a shotgun to kill a fly. The highway mileage is around 17-19 depending on speed. In town mileage however is deplorable. I have owned this thing for a little over a year and I doubt that it has ever seen the high side of 9 regardless of how I drive. Is this normal? This is the first LS engine I have ever had and do not know what to really expect from it. If this mileage is not normal is it possibly an engine management problem? I have plugged it into a scan tool and there are no codes, so either everything is operating within parameters or the ECM thinks that they are. The truck runs fine, has good throttle response and gives no indication of any problems. It just sucks fuel the way I used to drink beer in my 20's. If this mileage is normal the engine is coming out. If not does anyone have any suggestions where to start/