When I got the truck the engine was pretty tired, primarily due to a very worn timing set. As a result, I really don't have a reference to compare before and after the heads and cam. What I can say is the truck runs very well, and I do not have trouble keeping up with traffic accelerating out of a light or pulling 5th up a hill. It pulls strong above 2000 rpm, and revs well. Turner Engineering says the heads are good for 10-30% gains. Overall, I would not pull a good set of heads to replace them with high flows, but if you need to have them rebuilt, it should be something you look at.