It's either to much air or not enough gas. Sounds the same. If I'm driving down the interstate at 2800 rpm and put the pedal down, it will run great up to say 4500 rpm and then act like it's run of of gas. I can pull over, put the metal cover on and it will run like a top up to the rev limitor 6500 rpm. Doesn't make since because I can take the whole cleaner of and it runs great. Someone said it may have to do with the way the air is moving into the carb. I've got a Holley 750 with a ProForm main body (jets 74) with no choke.
Bob