MSD ignition power shortage?

Has anyone ever ran short on power for their MSD ignition (6AL) to the point where their car sputters on the track at high rpms?

First of all. I've upgraded to a 3G alt. on my 351W, 90 GT. (carbed). I've checked the output of the alt. and it is fine until I turn everything on (fan,lights,stereo and elect fan), then the output drops to about 12.5 volts.

I had a situation once where I had ran the stereo for awhile with the car off. It started fine, but when I gunned it the tach jumped to like 7000 rpm and the rev limiter kicked in and out with the car really only reving at about 3000rpm.

Once the battery charged a bit it settled down.

Last night, at the track, as I was staging I could see the tach jumping around like it did before every time I touched the brake. As well, I was gettting some sputtering at 6000 rpm. (not usually a problem-I shift at 6500).

I think it's the ignition. Also, not sure if this is related but the ignition was hotter than hell after a few passes. And no, its mounted on the fender, nowhere near anything hot. In fact, it's mounted right under the original air intake so it gets cool air blown over it.

I used the stock harness that came with the 3G alt.

Well I'm just using the stock ground strap from the block to the chassis.

I also talked to an MSD tech. He told me to make sure I didn't having any power wires or spark plug wires running near the ones between the ignition and the distributor....And funny enough, my coil wire is RIGHT there. That might be bad

I also heard a bad battery might be the problem. Mine is one from Costco that came with the car when I bought it!