It seems that my SE doesn't pull as hard from 5K to redline as I remember it once doing. It's not that it doesn't have good power, it's just that it seems like it really struggles after about 5500 rpm. Is this normal with age? Plugs, wires, cap, rotor, fuel pump, filter, air filter, cleaned injectors have all been done less than 5K ago. It also has full racing exhaust and a new RB muffler. Both ignition systems seem to be working properly, as I can see them clearly with the timing light. 6 ports open and close free and smooth. Any ideas?