Please Help Me!
As you can tell it could be alot of things I would start with the cheapest and work up until you figure it out. By the way a cloged fuel filter is also a possibilty. If its is a miss fire pull one plug wire at atime until there is no change in the way the engine is running when you find that cylinder strat with swaping the wire with another cylinder and see if the miss moves if it does get some new wires. Personally I am not a fan of Acell wires. I like ford racing wires for my mustang.
First things first, is the drive gear on your distributor compatible with your cam? (i.e. do you have a steel gear if you're using a roller cam?) I once had a roller cam and forgot to swap the drive gear and stripped it out. Since you say yours is getting better at higher RPM, one possibility could be with the advance on the distributor. For instance, if an advance spring slipped off or broke, your advance would come on too early but would still be okay at the higher RPM. Pull off the cap and rotor and make sure you see that both springs are attached to the mechanical advance. Do you have a vacuum advance?



