Is the engine popping or missing in high gear? These guys are on target with their suggestions on valve springs and fuel delivery. Ask yourself "how big are the fuel lines and how good is the fuel pump? Is the fuel filter too restrictive? And what's the fuel pressure at the top of second and third gears?"
If the engine has more than 1000 street miles or 20 or so full-throttle passes, then you need to have a couple of valve springs checked. Unless they're really high-quality springs, they go away really quick.