Anyone installed them? Did it create a noticeable power increase? I'm considering a set of Doug Thorley or Doug's Headers for my 1997 C2500 soon. I'd like to get a little more power out of her, since I believe at this point I'm going to end up keeping it instead of selling it. Figuring on an air intake, headers, fix the injector problem that is making it run rich, custom program, roller rockers, and maybe, just maybe a cam.