[aumoore]

Troy
I had a similar problem with my Explorer 5.0 motor with GT-40P heads and a trick flow cam. The motor would nose over at about 5500 rpm and I thought I was getting valve float. The Cam is supposed to peak at 5500rpm and I thought maybe the cam was just out of gas. I was running a Mallory Unilight distributor driving a MSD coil with no ignition box(the unilight will drive the coil without a ignition box).

I added a Mallory Hyfire digital ignition to help cure the rich smell at idle and it did clear that up. Now the motor will rev all the way up to the 6250 rev limiter in the Hyfire box(it is adjustable in 250rpm increments from 4000 to 10000rpm by changing dip switches) I guess the spark was not strong enough without the ignition box to support the cylinder pressure at high rpm.

Are you running a ignition box? It may be hitting a malfunctioning rev limiter or if no ignition box you may be blowing out the spark.