If this happened suddenly, was it just after a fill up?

I got some bad fuel a few years ago and it gave me fits for a month with poor power and black smoke. The only thing that finally helped was running a tank of B85 biodiesel through it on a good long trip. IIRC, it took 2 tankfulls to finally get things back to normal. Do you have access to biodiesel in your area? (less expensive a than significant volume of Diesel Purge)

When you did a diesel purge, it sounds like you disconnected the fuel lines and ran it directly from a container. Did you just run it at idle or did you do some revs? When your son changed the fuel filters, did there appear to be any kind of discoloration (primary) or was it crystal clear? Is there any indication of fuel leaks around the lift pump/primer pump?

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )