Jan (Connersmom): You have the 5.9L, same as mine. It was designed to run on the 500ppm fuel (best way I can describe it) so you may want to add some type of additive to the fuel for lubrication (removing the sulfur reduces the lubrication numbers of the fuel which impacts (might impact???) on the lifespan for things like the fuel pumps and injectors.
You are not alone on the service departments not knowing what is going on -- I cruise the turbodiesel forums for Dodge and take stuff to my dealer all the time -- they didn't know that there was a new fuel filter out or a technical service bulletin for those who have the outside cab lights (04.5 / 05 leaked and they changed the design - they will replace all of them with the newer ones if yours are leaking per the bulletin).
In any case, I've run both 500 and 15 ppm and can't really say I've noticed any difference -- again, it is hard to tell when you are fighting headwinds no matter which way your going (which seems to have been our luck recently
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One last thing (since I'm trying NOT to hijack this thread) - watch for water in your fuel. Another reason for additive. Diesel is like jet fuel - it obsorbes (spelling doesn't look right but I'm too tired to look it up) water from the atmosphere and then the water sits at the bottom. At the interface where the fuel and water meet, algae and other gunk grows. In jets they use an additive called 'Prist' (or used to anyway); almost all of the additives we can put in ours (PowerService for one) have water dispersants to help keep this nasty stuff at bay!.
Thanks everyone for letting me go so long.