I have a 03 ' ctd 6 liter.Started having problems with power.Rough idle and no power.Not all the time.Took a 800 mi. trip and three times had power issues.Running down highway and started losing power for a short time then it smoothed out.did this three times.Could this be filters?will filters cause this problem just some of the time.Could it be something else?

Which ctd do you have?:
CTD - Definition by AcronymFinder (http://www.acronymfinder.com/CTD.html)

Whichever ctd you have , if you haven't done a tuneup in a while, would be a good start, Plugs, filters, cap and rotor. You may find the problem at this time, and you will know what it Isn't.