I recently bought a 2006 6.0 with 62k miles. it recently started running rough and blowing white smoke. i checked the egr valve its dry. the exhaust doesnt smell sweet and im not loosing coolant. also upon cold start up i have no power once its warm it runs like crazy. Last i have oil in my coolant i think it could be the stc because it is completely stock. any ideas i want to get it fixed before i do thibgs to void my warrenty

 

Oil in coolant can only be from a ruptured oil cooler, if you are lacking power on cold starts you should first test the FICM, there is a test procedure at the top of the 6.0 section

 

Ok and when I'm idling or driving anywhere between 1250 and 1750 rpms it feels like it gas a missfire. This doesn't happen all the time though. And it lags on power until 2k rpms