My engine is breaking up at around 3k rpm.

I changed the plugs, wires, cap, rotor, and swapped out my msd 6al box with a buddys. Still having the same issue. Any advice?
The only thing I have not done is adjusted the rocker arms (1.5).

Has anyone else experienced this? Besides this issue it is running great.



440
727

MSD distributor/MSD 6AL
Holley red pump/-8 line/800 holley (6lb psi)