[TButtrick]

I'd be focusing on #3 plug. Try swapping #2 and #3 wires and take it for spin. Now see if #2 is fouled as #3 was. If not, you might try checking exhaust and intake lift per cam specs on #3. Take a REALLY close look at the rockers and valve springs on #3. Broken springs/bent valves/worn lobes can still give a positive compression check (at this stage) as your problem manifests iself at higher RPMs. Even with a completely broken valve spring, you can still have a positive compression check. A leak-down test on #3 might reveal a problem.

Your problem is most likely isolated to #3 and behind the dizzy (but not excluding the cap/rotor) BUT I've had a nightmare of problems with a 6AL. MSD quality does not parallel their marketing. The voltage source to your MSD has to be clean and at full potential. You can easily check with a DVM to see if there is a voltage drop across the source. Hook up one lead to the originating source to the 6AL and the other at the input to the 6AL. There should be no voltage drop across the source (zero resistance). I tossed the 6AL and stuck with good ol' Petronix after the box disintegrated. BTW, there IS a way to bypass the MSD 6AL. Do a search. It's out there.