Troubleshooting help/suggestions

[Coloradocobra]

I'll try to be brief but thorough. I have a 428 that makes gobs of power up to 4000 RPM but then the HP curve goes flat and the torque drops off. It runs great but falls flat on its face. I know it's not a small block - but a 4000 torque peak cuts into the fun factor. This has been shown on two chassis dynos with two carbs. Here are some specs:

428 .030 over with stock crank, stock peened and polished rods.
Weisco forged pistons with dish for 10.8:1 compression
Dove F5 heads with bowl blending, 2.09 intakes
Dove rockers
Crower "hydraulic hauler" 280 HDP cam with 280/288 advertised, .550 lift, 108 degree lobe center. The cam was degreed and set "straight up".
Blue Thunder dual plane med. riser style intake
Holley 750 vac. secondaries - professionally built for Denver's altitude
Pertronix/MSD ignition setup with re-curved distributor - 32 degrees total - timing verified on dyno

The dyno test shows good fuel pressure and mixture throughout the rpm range.

The torque and HP curve would be great in a tow vehicle but with the cam specs, etc., it would seem that I should see peak torque at 5,500 or so, not 4000.

Plans this winter are:

1. Bench flow the heads and port match intake and exhaust
2. Switch over to solid lifter cam approximately 288 degrees
3. Possibly install larger diameter valve springs to eliminate possiblity of a float issue.
4. Replace the mechanical fuel pump with electric

Valve float often creates a "dip" in the curve over a short rpm range but this is just a steady drop.

Things I don't want to do: Hydraulic roller, solid roller, change carb

Am I missing anything? I'm not looking for thousands of HP but with the above combo, it seems that it should pull hard up to the mid 5000's. It will hit the rev limiter at 6,000 but it seldom sees that because when drag racing I short shift at 4500 to 5000 to get my best times.

Thanks in advance for your help.

Gary