I can vouch for the Weiand Stealth manifold, myself. Great power from idle (600-800) to 7,000 RPMs. I enjoyed it (when I got to drive my friend's truck who bought the manifold from my when I parted out my motor). If you're looking to swap your cam, too, though... get the Edelbrock cam/manifold package. Great parts and the guesswork is already done for you. Just get the matching cam and manifold (then the heads, when you get bored
) and you'll definitely notice the difference.