My truck (late 04 standard cab all stock no mods of any kind) is having the seame issue. I did see a low boost code but that is it. I cleaned my EGR valve and checked voltage at the FICM Looks fine. Problem is I have no gauges just the OBDII scanner. Did you find the problem?

 

I still have not removed the pump yet. I just stare at it and hope that the problem shows itself to me, LOL. I hate to start changing parts with out a for sure diagnoses.
IPR looks good. No damage to screen.
I am doing an EGR cooler delete (got one on order from Custome Diesel) while I am there but, havent decided if I am going to change the oil cooler yet. I have not had an EGR cooler failure yet. 130K miles so I figure EGR cooler delete is a must even though the round style that I have is not prone to failure as much as the newer ones.
AE did not show that any of the cylinders were missing before I started disassembling. Seems like if I had an injector with a bad O-ring it would miss on that cylinder when it started leaking??
I am wondering if it is still possible that I have a bad IPR. I did comand it to 100% with the AE tool after I pulled the turbo off while I was testing with air thru the ICP port. and there was no difference. I could still here the air sound at the turbo drain port at 100% and at 0%. What I don't know is if there should be no air passing with the IPR at 100%?
Now with the cover off and testing thru the branch tube on the top of the pump the IPR is out of the equation, but blade35 you are right I can only test to 120 psi.

 

Here is the latest update. Whoo Hooo truck is back in business!! Of course after many hours of labor and diagnoses. New HPOP, new HPOP output tube, new IPR, new ICP sensor. I also threw in a new oilcooler and installed a custom diesel EGR cooler delete kit. I never did pinpoint the problem to the HPOP because I could not bench test it, but I have a pretty good idea that it was the pump based on the way it felt when I rotated it by hand. AE is showing pressures up to about 3600 psi now at WOT.
I also cut open my old oil cooler for my own curiosity. I have posted pics in my gallery under the HPOP folder. Surprisingly there were no signs of plugging in the oil cooler. Not sure why not at 130k miles.
Gonna have to add some lines to the "you might own a 6.0L post now". LMAO!
I would also like to send out a special thanks to all who offered help and advice on here. To mention a few, npccpartsman, cheezit, blade35.........thanks a ton and hope I can repay the favor some day.