99 W900 KW 3406e cat

Hello everyone, I hope all is well. I have a little issue with my 99, W900, the truck under a trailer started jerking like choking, no check engine light is on, I tried to do the diagnostic with crus control is giving me 5 flashes, pause, and another 5 flashes. Fuel pump is about 1 year old, fuel pressure was between 90-100 psi prior the problem, checked it with gauge while driving it keeps bouncing between 40- 60 psi. I parked on the side checked it again and it was between 20-30 going up to 70 and back to 20 psi so it was not steady. Any idea or where to start to figure out this issue? Thanks in advance!

 

I replaced them but didn’t fix the issue

 

It fires right up, even when idle the engine runs very smooth, only this started yesterday, drove about 300 miles with 46k on weight, I exited the ramp and it started this issue for few seconds and went back to normal until today; it drove me nuts

 

Where is that valve located?

 

It’s 1wl