No, earlier 12 valves are actually fine. Your horsepower is going to come from how your P-pump is set up and making sure your turbo(s) push enough air to match your fuel. A cam is a good mod, but they are more for extending the RPM range you make power in and improving air flow, subsequently lowering EGT. The 1997 and 1998 5 speed trucks come with a P-pump that flows fuel pretty well in stock form. Look for the number on the tag on the pump for the model number. It should end in 887 or 913, denoting a 215 hp pump. Putting a performance fuel plate like a #10, a 4KGSK, 191 delivery valves, some performance injectors, setting timing up to 17 degrees or so, and then getting a turbo that will flow enough air to burn the fuel you're feeding will put you well on your way. But if you have a manual shift, you will need an upgraded clutch. If you have an auto, it will not last long stock. I'm sure other more experienced people will chime in. I haven't been messing with these engines very long.