I am late on this one but it looks like CChase is leading you in the right direction. Change the FF, and see if things get better, also look for diesel fuel in the coolant, there will be a slime on the top of the degas bottle. BTW, you can replace just the O rings on the injectors, you don't have to buy new ones, although with that many miles I would at least have them rebuilt, but that's me!!
NCH