isx 15 fuel pressure drops when boost passes 15#

[Rockyvalley]

isx 15 appx 955000 miles fuel pressure 29000 until the truck starts boosting to 15 to 20 pounds then drops to 6900 pounds. starts and runs fine. new filters pump head and relief valve on head. any help appreciated. Thank you.

[Rawze]

So what is the issue?... fault codes?... low power?... your post there is a bit vague.

Also, will it pass a leak-down test exactly like this video shows?... what was the leak rate in 60-seconds?.
ref: https://rawze.com/forums/showthread.php?...3#pid75483