I had a simular problem shortly after i bought mine. Would do fine for a while then in 4th or 5th gear would start missing real bad. I would down shift and she would do just fine. shift up to next gear and would be okay for a while then end up down shifting. I tried to find my old posts about it but no luck. I changed the filter,fuel lines,pulled the fuel tank out twice and cleaned it, changed spark plugs,wires and cant remember what else but nothing worked. I got a good price on a new ECU so i decided to try that and have had no problems since.