03 with 18 psi at degas on startup

I'm new to the 6.0, but I have done my research on these trucks. I am losing coolant out the top of my degas bottle. So I bought a cap and new degas bottle. Don't stop the loss of coolant. So I read all the info I can find and it says EGR cooler or head gaskets. My truck is studded, with a welded EGR cooler, so I decided to do the head gasket test using the gauge and hose run in the cab to watch the pressure. On start up it goes straight to 18 psi, and it says the psi should go up while driving not right at start up. I cannot and have not found anything or anyone with these symptoms. Has or does anybody know what's wrong? My guess is head gaskets, but I don't want to do all the labor when it might be something simpler.

You have a head gasket problem, the job probably wasn't done correctly the first time.

Imo
Any 6.0 that blows out of the coolant tank needs a proper delete, stud and gasket job.
A new bottle and cap (if it stops the problem) is 99% of the time just a band aid anyways.