If the power is dropping off as the boost increases, that suggests to me you've got spark blow-out. - I've had that problem when the plugs were gapped too small, but it's an easy and cheap fix to regap them.
Which plugs are you running? I'm a convert to getting rid of the precious metal tips and going back to "standard" copper plugs.
Which plugs are you running? I'm a convert to getting rid of the precious metal tips and going back to "standard" copper plugs.