Hmmm.... starting to be a common issue I see. Mine does the same thing! And I have done the same things you have!! FF, lots of fuel cleaner, cleaned pre-heater, new OFV.....
Do you seem to notice it worse when the truck is up to temp?? Mine seems to be worse when its up to temp, and does disapear after like 1800 RPM. No smoke what so ever as well. Guess I am going to be ordering a big line kit this week.

God I hope it isnt my injection pump!!!! 1 I dont like my local diesel shop, 2..... I aint got the money!