I had a some what similar problem. I also have a HO. Turned out to be the pop off value. Toward the end wouldnt go over 200 psi. It is on the back top left of the machine. The peace inside decenigrated.
I have an extended 2500 express. It has windows in the barn doors. I love the windows. It helps you see on coming traffic when pulling out on busy roads . Great safety feature IMO. I have the perforated vinyl over the windows. You can see out great but not in.