Calling all D12 experts, getting a derate condition with no codes

Hello all, long time lurker first time poster.

First off, thanks to all of you who have posted in the past, it has made the ownership of my truck a lot easier and cheaper and I need your help again.

I have a 2004 Volvo VNL daycab with a 465 hp D12. I am getting a derate condition with no codes. Truck runs and drives great but if I punch the throttle at 1400 or above, it will derate with no codes. It will reset to normal when I turn the truck off and re-start it. If I punch it at 1350rpm, or take 4-5 sec to roll into the throttle it won’t derate. Just derates when I punch it.

Boost is good, no leaks. 35-38 psi full power, no derate, 28-30 psi full power, derate.
Average fuel mileage unchanged from before this started till now.
When derate happens, instant fuel mileage will go up corresponding with reduced power. ( ie top gear 3.5mpg full power no derate becomes 4.3mpg on derate.)
Changed fuel filters, no change.
Changed fuel pump due to bad accessory drive gear bearing, no change.
Changed fuel pressure regulator after checking it and it would pop off at 45 psi, no change to derate, did run smoother at full power.
Changed turbo boost/temp sensor, no change
Checked fuel return line for bubbles, no bubbles.
Pressured fuel tanks to check for leaks, couple psi of air for 20 min, no leaks.

Nobody around here has vcads software, dealer is 2.5 hr away.

Any ideas?

 

I have thought of buying the vcads software since I like to work my own stuff. I see you can buy vcads software online, is that stuff any good or where else would I get it?

What version would I need?

 

Truck gets used fairly regularly. I can hear a distinct change in sound when it goes in and out of its warm up faze and engine brake works on both stages.