If you changed heads and cam, and it's making more power, you need more fuel to feed it....
It's lean...
Another thing that can cause crappy performance at part throttle is the lack of an air cleaner, or air rushing over the top of the carb, throwing the air bleeds outa whack.
Did you remove the hood? Did you take off the air cleaners? Change anything on the induction side other than cam/heads?