There really isn't that much of a restriction in the exhaust. You can only move so much air through a naturally aspirated engine(volumetric capacity). It's the atmospheric pressure that moves the air into the engine, and as was mentioned it's the TB, Intake manifolds, and heads that limit anything, but then again, an engine can only hold a certain amount of air in each cylinder, so what that point of shoving air down there, when it would make a difference. The best way to gain performance on your 3.0 is forced induction(supercharge or turbocharge). This compresses the air into the cylinder, and increases the pressure. This will yield power. Don't believe the flase performance hype, they just want to make money. Another good option for the 3.0 is the 5.0 roller rockers that bolt right into place on the 3.0. They decrease valvetrain friction, increasing the feel of acceleration, providing longer life of the valvetrain, and runs smoother and more quiet at high rpms. Always remember the 3.0 loves high rpms. It can easily handle them to, don't worry about hurting it. Assuming you have a manual, when shifting wait till 4,000, when you shift it'll keep you in the power band, which is largely above 3,000 rpm. If an auto is what you have, a programer (not a chip) will help cahnge the points at which your auto shifts, increases the feel of power, and giving your truck better acceleration. Ford hadn't quite figured this out on the 3.0 and made the auto's shift too soon for the 3.0 to reach it's power band.