Easy way to locate leaks in your system...
Charge the entire thing to ~30 psi, and listen...
If no hissing sounds, pull the gas locks from the kegs and turn off the tank.
Check the regulator an hour later. If it's not moved, check it again in another hour, or in the morning. If both gauges haven't moved, you're leak free (24 hours is the ultimate test).
Every time you alter your gas configuration, charge the entire system to ~30 psi and listen. Then turn off the tank valve and see if the high pressure gauge starts dropping.
If you keep the tank in the fridge/freezer, the high pressure gauge will read lower. It will still dispense the same amount, you'll just get a lower reading on that side. I keep my tank out of the fridge (more room for kegs that way).
I did have some leaks that the above methods helped me to hunt down and eliminate. I had to tighten up the worm clamps on the gas lines to eliminate them. Not a big deal, just be careful to not go too far there.
I used the same method on the 20oz tank and regulator setup I have (charged to 30psi and waited).
I would also make sure you have the small plastic items on any manifold fittings you have. Unless they're tipped so that you don't need those of course. I quickly discovered forgetting to use one of those the last time I altered the setup. Easy fix, just gave me face-palm...