Air pressure weirdness

Been dealing with this for a few days now:

Sometimes air builds very slowly (have to rev at 1500 rpm for it to build air at all). At other times, it works fine, builds air even at 600 rpm idle. Seems to work fine in the morning, but then starts getting weird after driving for a couple of hours.

This started a few days ago in Illinois, when my governor froze up and pressure went up to 160. Replaced the governor, and it worked fine. Next day the slow air pressure building problems began. I thought it might be the cold weather causing ice in the system, but now I'm in California, it's 50 degrees out, and it's still doing it.

I do not hear any air leaks. No air loss when truck is off. I tried to bypass air dryer as a test (disconnected its' in and out lines and screwed them together), but it didn't help. I thoroughly drained the tanks (even took off the fittings to make sure everything blows out completely).

My air compressor is pretty new (replaced it in October). And everybody tells me air compressors don't fail like this, intermittently. They just crap out.

Other clues:

It sorta seems to start working normally after messing with the lines. I took it to a TA earlier today, and they were clueless, but they disconnected the air lines from the dryer and it magically started working good again. When I messed with lines a couple of days ago, it didn't fix anything immediately, but came back to life like an hour later.

The governor is still being weird, at least once - yesterday, coming down that long easy grade from Kingman AZ to Needles, pressure went up to 140 again. At other times it's fine, puffs out at 125.

This is really hard to diagnose, because as soon as I get to a shop and they call me in, it starts working fine again. And I don't want to go replacing the whole air supply system one piece at a time as an expensive sort of diagnostic. Could it be something weird with that new governor? Maybe defective part or something? Or maybe the air supply line into the compressor? The load/unload valve on the compressor sticking halfway? (if that is even possible)... Any other ideas?

 

All good points, but it would have to be a really bad leak to equal a compressor at 1200 rpm (about the break even point). And whatever air it does slowly gain, it keeps. So I'm thinking the problem is "upstream" of the tanks.

 

I'm gonna have to try that, I guess. A governor is only like 20 bucks and is simple to replace. Pretty cheap way to start the whole "diagnostics by replacing everything" process. And if it's not the problem, at least I could always use an extra governor in my spare parts pile.