Won't run past 3500 rpm

[Southtowns27]

I have an 8CM in my truck with about 500 miles on it since being built. It's a stock rotating assembly, bored .060" over, with a Schneider S100 cam, Isky springs, and adjustable lifters. Offy heads and intake. I clayed the engine when it was built so I know the clearances are good. It won't run up past about 3500 RPM. I can ease it up to that speed, but if I try to make it run faster it drops a few cylinders and actually slows down. I've also noticed that if I whack the throttle it also seems to drop a cylinder while it's winding up. It'll cruise down the road at 55mph no problem though. At high RPM vacuum is about 22 inches and fluctuates maybe an inch. Compression is about 125psi and they're all within 10psi of each other. Things I have tried so far: Different plugs, plug wires, different timing, condenser, swapped the Mallory dual point distributor for the stock one, it had Speedway "97's" on it, swapped those with new real Stromberg 97's (2psi fuel pressure, .043 jets, 69 power valves), reset the valve lash, different plug gaps, disconnected all the vehicle electrical and ran a jumper wire right to the coil, different coil, unhooked the wiper vacuum, unhooked the PCV system.
NO CHANGE.
What am I missing here???????