I just gave it a full tune up (plugs, wires, fuel filter, air filter, distributor cap and rotor). The truck also had a new distributor assembly installed. The truck ran rough when cold started since I got it. It will start right up, but will run rough for a few minutes, until you start driving for about a mile, then it runs fine. The truck runs very rich also, I can smell gas coming from the exhaust (new cat back exhaust also). There is no check engine light. Could the coolant temp sensor be at fault, even though it looks like it has been replaced before? Could it be the O2 sensor?