2007 Pete, with cat c15 nxs04784 losing boost

All the basics......
Get it on a laptop first. CEL bulb in dash could easily be burnt out.
Fuel pressure, dirty air filters, exhuast leak, cracked bellows are easily missed at the turbo, when was the last top set done, restricted mufflers, air in the fuel, leak in the charge air piping, ect
Cats should be 50+ psi, your boost is quite low. Any noises, misfires, recent work done......
Lots of things could be wrong. Gotta start eliminating some of them

 

Won't need a laptop, when you turn your key to the on position the cel should light up for a second the turn off, this is how you know the ECM is connecting.

Odds are you have a cracked bellow, very good chance if this..... One on the inside of the turbos likes to crack and is hard to find. Twins make a little boost idling so idle at 1000 and soap and water or just go get a shop to pressure test the turbo assembly.

 

CEL = Check Engine Light

 

If you're new, take it to a shop and let them figure it out. You're probably not allowed to work on the company truck anyway.

 

That's normal if you think how turbochargers work, they compress air so air density changes charge air pressures. You will have more boost in Canada cold winter then you would down in warm Texas cause the cold air is more dense.

Boost leak, test it, find it, fix it.