I have a 04 pontiac Grand Prix 3.8 engine my car was overheating so I flushed my radiator and took my thermostat out that worked well for a week or so also my upper intake manifold was replaced I have white smoke coming from my exhaust now it feels as if my engine wants to give out on me when I'm in traffic at a light is it time for a new head gasket or do I just need a tune up, oil change etc