I think you an I might be in the same boat. If you look at my post, "HELP, what did I screw up," I have what sound like to be the same exact issue. Unfortunetely after reviewing the non-serviceable plug instructions, I do not think I installed the check ball correctly. If you refer to diesel o-rings website for the plug replacement, I am pretty sure I did not have the HPOP in the correct orientation when I re-assembled it.
I really dont want to, but it looks like I am going to have to tear everything back out to fix this. Hopefully I didnt ruin the check ball or anything else. I am pretty sure this is my problem, but please private message me if you find anything else. I will let you know if that fixes my problem.