1995 Ford Mustang Poor Performance

I have a '95 V6 3.8 Mustang with approx. 200,000 miles. Recently the engine has begun running ruff, with low idling RPMs, around 500-650, and sometimes stalling. Also, ther is moisture and white 'smoke' coming out of one of the rear tail pipes. (It had an inexpensive dual exhaust installed). When accelerating it'll occasionally have abrupt lags or catches. The check engine light came on with the code reading a bad cam shaft position sensor, I replaced the sensor and cleared the code but still the light is on saying bad sensor. I'm afraid it might be a 'bad' piston b/c I also have a problem with the engine overheating and coolant boiling up out of the cap. So far I have replaced the Cam sensor, the thermostat, temp switch, temp sensor, fan motor, and the radiator is only 6 months old, next is the water pump. Am not sure if the overheating and engine problems are related or seperate or if i am on the right track. Could use a second opinion.