Replaced the lower cap on the distributor and it didn't help with the miss. Starting to look into the fuel pump or clogged strainer. It doesn't miss all the time runs good then when I give it a little more gas it starts missing.
It does sound like ignition to me. I bought a brand new cap once which looked perfect, but caused a high-rpm miss. I replaced it with a Ford cap, and the miss was gone. I wouldn't expect that problem with a MSD cap, but you never know for sure. If you have a spare cap around, I'd throw it on and see what happens. Sometimes parts are defective new.
When did the miss start? Did it start right after you did some work on the car?
On a car (not mustang) I once owned, it ran perfect, until I really got into the gas (more than 3/4 throttle or so), and then I had a nasty miss. After a lot of checking, it turned out one of my spark plugs had a VERY small crack right at the base of the porcelin. Usually the plug worked like normal, but when I would punch it (spark energy increased?), the spark would start jumping through the porcelin and grounding out into the head through the plug base.
It's pretty easy to crack a plug if you are using a plug socket without the rubber donut in it, and you would never even notice. It might be worth checking your plugs VERY carefully if you haven't already.
I agree with Hissin that a fuel pump problem is unlikely to cause a random miss, but I suppose anything's possible...
I'd rule out every ignition componenet first though.
EDIT: I just read your other post and saw you replaced the plugs already.
