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Is it possible you have a large leak between the compressor and the tank? I would check the drains and sludge valves also. If you have a large leak you will not here it when you shutoff engine as pressure is gone as soon as engine stops.
Remove the tanks supply line from the compressor and hold your had agiast it with the engine running. You will not feel a lot of pressure but, you should feel some.
If you can connect shop air pressure to the system at this line, it is easier to find a large leak.
I also had a check valve at the first tank stick open and it would not let the tank pressurize.
If you add air to a secondary or dry tank another check valve will prevent air from leaking out the primary or wet tank.
You have two secondary tanks and that is the pressure you see on your gauges. The wet tank is not connected to any gauge. That is why you need to add air at the line from the compressor. This will check you whole air system and the dryer as well.
I have missed this step before and wasted a lot of time only to find the supply line broken in the frame were I could not see it.
Governors have several plugs that need to be added or moved.
If you still have the old governor double check the location of the plugs so you don't have any in the wrong place.
Make sure you did not cross the line from the wet tank with the line from the dryer.
The tanks have a weld in baffle that seals the sections. You can tell it has two sections by counting the drains on the tanks. My truck is a single tank with three sections.