Lately my 5.0 has been cutting out at around 4k rpm, like there is a dead spot and then picks back up. It only falls flat on its face like this when the car has been running for awhile. It just recently started doing this. I have already put in plugs, wires, cap & rotor, k&n, fuel filter, pcv valve. In another words a pretty complete tune up. I have been running 93 octane lately too as I have the base timing set at 14*. None of this has fixed the problem. Who can help me solve this?