I searched and didn't find any info so I decided to post:

When I run the engine up past about 5,500 RPMs the headlights and dash lights will dim. The only time it happens is at high RPM.

I'm running a Summit HEI dist. and the alternator has less that 10,000 miles on it. The battery is also fairly new. I am also running an alpine amplifier straight to the battery.

I'm thinking either an aftermarket HEI ignition module or maybee a digital ignition box (6AL etc.) might eliminate the problem.

Any Ideas?

 

I highly doubt it's the ignition system drawing too much power. It seems to me that it's the alt's rectifier or regulator not being able to handle the high rpm (= high frequency).
I noticed this effect in a rectifier/regulator I built for an outboard engine. To my surprise it quit charging altogether above a certain rpm. I figured it had to be due to a too high turn-off time in an opto-coupler I had used in that design. The same issue would apply (at some point) to transistors used in alternator regulators.
Unless you run at 5500+ for extended periods of time I wouldn't worry about it, or you could install some underdrive pulleys to fix the phenomenon and get some extra hp to go.

 

first I would check your grounds, then I would fix your sig since it is way tooooooo long.