Update...
I hooked up everything again, charged it up with CO2, took readings from every gauge (including the keg pressure via a keg pressure gauge) and turned off the CO2 tank. Overnight I lost 0 psi.
The only real difference with this test was... I turned the CO2 tank off on the tank itself, not the shutoff on the regulator. I don't know why that would matter. It's leak free, but I'm stumped as to why the tank being on would matter.
