HPOP problem, need advice
Alright this is a long story so bear with me,I work on helicopters for the air force and am mechanically inclined but I do not feel like I could do this on my own. I bought a 6.0 diesel about 3 months ago, the truck ran good up until about a month ago. I took it to what i thought was a good diesel mechanic. He ran a test and said I wasnt getting enough oil pressure to my injectors, 200 psi. So he changed out the IPR, and it ran fine for two weeks. I got bad diesel and it clogged up my filters, he changed them and it idled and then died. He then ran another oil pressure test and told me it was only getting 500 psi on crank, but my fuel was fine at 55 psi. He said my HPOP was bad, and quoted me $2400, including 16 hours of labor (BULL****). I am now in the process of towing it to another shop to get it done for $1400. He told me it needs 1500 psi on crank oil pressure wise. The shop that its getting towed to is highly recommended by all my diesel buddies. The shop wants to run a $300 test by pumping 2000 psi of nitrogen to find the leak. He is saying that it might infact not be the HPOP. Do you think I need to run this test before forking out 1400 dollars for the HPOP? I would hate to spend the 300 dollars on the test and its the hpop but on the other hand i dont want to change the hpop if its not needed. I need some advice bad, i would appreciate any.