Air Compressor ??

[Grizzly]

Most nights I lose all my air. I have yet to hear an audible leak and other nights I might only lose half my air. However lately I've had trouble building air idling with the pto kicked up. I thought it was the air system on the trailers I use robbing me of air but it does it when I'm unhooked too. Some mornings or given enough time it will build air. Others it won't start to build air until kick the rpms up to 1200. Once I start driving its ok. If I stop and set the brakes on the trailer or tractor, either or, or both I will drop pressure. Like when sliding tandems and you have to set/release them a couple of times. Rev it up, build the pressure back up and good to go. Doesn't lose sitting at a light either. Just over night and trying to drop and hook or slide tandems.
Am I missing an air leak somewhere?
Is my compressor going bad and need replaced?
Something clogged I don't know about?
This? that? the other?