<VV> PG engine break up at 4400 rpm

[Michael Kovacs]

 I will be running my PG 140 at the New York Safety Track again this year. Last year when accelerating down the straight in low, the engine pulled well until about 4400 rpm where the engine seemed to just stop accelerating. 
(heads milled to .035 squish, balanced forged pistons and con rods. OTTO 20 cam, etc.)

  I am running igniter ll and the recommended  flame thrower coil. I just changed the spark plug wires to 8mm and new AC 44F. Timing set at 16. running 87 octane.  Same  4400 results in test run yesterday.
 My Fitch with similar internals, I can shift at 5500 with ease with it still pulling.
Any ideas??