my cobra started to feel like it hits the rev limiter at 3500 rpm and the tach goes crazy and i hear the car sputtering but as soon as I let of the gas it stops .I changed the ignition coil ,TFI module even the distributor (i have the stock parts) and still have the same issue .This started after i moved my timing down a little because i was hearing piging it was at 14 degrees got it down to 12 then to ten with the same result .Any ideas what could be wrong the only thing i can think of is the spark plug wires the plugs were changed about 8000 miles ago with motorcraft stock replacements.