120 lbs air exhausts to 100lbs

We have a 2000 XLII LeMirage Senators coach with a Vulcan Conversion. Recently we had a problem with the ride height and the A-Tank not holding pressure. I found a small leak from the 3rd Norgeen valve so I purchased the rebuild kit from Prevost and rebuilt all 5 just to be safe, figured if one started leaking another was soon to follow, any way the leak stopped and I can once again raise the front end, but the ride height doesn't appear to be normal as the front tires rub the styrofoam wheel well when turned. I have also noticed the A-tank gauge gets to 120 psi then I hear it blow off In the rear wheel area the pressure then drops to 100 psi and slow rebuilds to 120psi. I have sprayed a soap solution on all the air line fittings I can see and can't find a leak. I don't remember this happening before and tend to believe my ride height issue is the lack of the a-tank keeping 120psi. Thank you in advance for anyone's help on this.

You have an air leak somewhere in the system. Not necessarily in the areas you have been working. Your pressures are normal cut in and cut out numbers. Keep looking.

Just a guess but could the air dryer valve be hanging up in the open position? Should be easy to check and replace.

Since it sounds like it has "just started" might check the ride height adjustment arms, to make sure that it has not become disconnected somehow

Thank you for the responses. I will look into the purge valve on the air dryer once I locate the air dryer :D

You may already know this, Be sure to have your Coach properly supported before working on your air system. Not your axles, but the Coach itself.