If you're not going to upgrade the truck then the stock fuel system should be just fine, I've had no problems with ULSD. Replace the fuel filter, and check the bottom of the fuel bowl for sediment in the bottom. I took mine all the way out and cleaned it, I would also clean the FPR screen while your there. Look at your oil rail plugs, if they are seeping change them out, if one of the o-rings blow you may not be able to start the truck. I got them for almost $8 each from Ford, they are $21 at IH for the same part. Also look at your turbo pedistal o-rings, your turbo up pipes, and your EBPV valve if you have one. Depending where you live you may want to change the glow plugs, I got a full set off of Ebay for $50. DO NOT buy anything except Motorcraft Beru's, they are the only ones that last. Cheap ones can swell and if they break you could end up pulling the head. I would at least upgrade to a cold air intake and exhaust system, it will help with milage, the truck may already have them though. Have someone you know with a scanner pull the codes from the truck, that will give you some good places to start with fixing stuff so you don't get stranded. You're HPOP is most likely fine, you'll know if it is having problems, they can run up to $800 but you can find them for much more reasonable prices. I've heard of no problems with the ZF6.
