'85 GT 4V Breaking up past 4500 rpm

[Mgino757]

I have a situation with my '85 GT. At first, this was only happening in 1st gear. Now it's happening in second gear at WOT. I'll mash the throttle, it'll accelerate up to around 4500 rpm and then it'll stop pulling completely. It'll act like I'm hitting a rev limiter, even though I know there isn't one. I'm running the original 4180c with a secondary metering block and #73 jets. I have #63 jets in the primary block. I have a brown Holley secondary diaphragm spring, which starts opening the secondaries around 2700 rpm. I upgraded to the center hung LeMans style fuel bowls with the levels set to the bottom of the sight plugs. The fuel pump is new. I am also running the stock distributor that I've recurved. My initial timing is at 14°, all in at 2800 rpm at 35°. The coil is also a new, stock replacement.

During a WOT pull and hitting my 4500 rpm wall, if I let off of the throttle a bit, it'll continue to pull until about 4900 rpm, if I let off a touch more, it'll go to 5100 rpm until there isn't enough airflow to rev any higher. The only thing that isn't original is the ignition module, it is a replacement I got from Advance Auto about 10 years ago when the original crapped out entirely one day. Before, it would pull up to a little over 5500 rpm, which the cam and heads were tapped out at that point. I've checked anything simple and stupid up to the point of considering a parts cannon.

Any ideas? Would a failing ignition module act like this? Fuel filter is clean, no debris to be found. Plugs, wires, cap, and rotor are brand new. Plugs are gapped at .045".