Pressure building and purging issues

Hello everyone,
My problem has started ever since I got my transmission rebuilt. After that, I went on the road and I caught an air leak. I came back home safely because I couldn't find anything on the road and found a leak underneath the air module. So, when I found the leak, I got it fixed, it was actually an air piston range that was leaking. Everything was put back together, and my mechanic didn't want to start the engine yet so he pumped air directly into my air tank, to check for leaks without starting the engine. At first, he started pumping in the third tank because he didn't know what tank to pump in, and no air came into the system so he pumped into the primary tank. We tested for leaks and everything was perfect when flipping upshift and downshift.
The next day I was picking up a load and I noticed that I was losing air, so I found a place to park before my brakes locked. When I stopped my truck, there wasn't any leak. After I restarted my truck, it started leaking air again. So I looked and found that my purge valve was leaking like hell. I took the purge valve off to inspect it and found nothing wrong, so I put it back. Then, the pressure started building but not purging!
I replaced the governor, the compressor unloader valve, and completely replaced the air dryer. The interesting thing about this is, sometimes, when I start from an empty tank, it charges air like its supposed to and purges like its supposed to, but when I release air with my brake pedals, the pressure doesn't raise up again unless I pull out a discharge line that comes from the governor to the air dryer and the pressure starts to build again. When I pull this line out of the air dryer, it spits air like there was pressure in it. When I put the tube back, it purges like it's supposed to. But, then my truck eventually starts pumping air only, without purging. My compressor is only two years old as well.
I feel like I've exhausted every option and wanted to know if anyone knows what's going on? This all started after I got air pumped into my tanks so I am suspicious that has something to do with it.
Thanks everyone so much!