[rdlamb]

Hi Art; You might also check your drain valves. The air line has a couple of drain valves to drain moisture from your air system. If the dealer 'cracked' them to drain moisture without fully tightening them you will get a gradual bleed off of air.
Also, you have a dessicant dryer on the airline. While having your brakes checked (you should have a pro do this, nothing is more important than your brakes), check the dryer.
Finally, you have air bags. A leaky bag will drain your air system, which unfortunately, decreases your braking. Check these as well.