The main problem is the engine running on 3 cylinders. The problem began when cranking and warming up (ran on 3 for about 5 minutes then leveled out). I inspected spark plugs, wires, dist cap, and rotor only to discover badly worn dist cap and rotor. I did not replace anything until it began to run rough and never "leveled out". I have now replaced dist cap and rotor as well as checked all wires and coil (nothing wrong). Last year, I had the head rebuilt after blowing a head gasket. Also, I had the seal replaced under the distributor due to bad leak. Since the head rebuild, it has pinged when going uphill or under heavy acceleration (the timing is set to factory settings and running 89 octane gas). I would like to know what to check first. Distributor? Valve sticking? The engine has 250+ miles and burns no oil, so I wanted to keep it running. I have considered replacing with a motor of less mileage though. Any help or ideas would be greatly appreciated!