We all heard of "short shifting" back in the day. Well we tried that, 4500 4800 5000 5200 5500, never, ever, picked up ET till we went back to 6800, this was on a very mild 440 with stock 906 heads. My 383 wouldn't Et untill it was turning 6500. The Max wouldn't freight train untill 6500, 7000 thru the lights. Whole lot of BS thru the years that's repeated. It's all in the setup.
Might add, all non ported heads.