[rvguy]

I have been thru all of this with coach 480.  Listen to Richard and the other gurus who have the older coaches, they will guide you in the right direction. I fought this on my coach several times thruout the repair process.  Rebuilt 6 packs, repaired all air leaks, replaced all air bags, .  I did come across a issue that I want to share.  First off  engine running , hit the travel button. Go to the rear of the coach and check the  forward solonoids( nearest the firewall, these are the travel solonoids) put a washer on there and see if it sticks. If so pull the airline off the back of the 6 pack block behind the travel solonoids and see if you have coming out of the lines. If only one side has air coming out of it, I suggest looking at the 2 check valves located at the other end of the 6 pack block.   
On the far end of the 6 pack block, on the top and bottom, there is a brass plug. With all air dumped, pull those 2 plugs off , under that is a small spring and a plunger. I found that mine was sticking causing air to sometimes go to the bags and sometimes not. I tried cleaning, but they would stick again. So pulled them out, put the plugs back in a BAM. all issues went away in the rear.
Furthermore- I have been a master rv tech for almost 35 years as well as a heavy equiptment mechanic all my life ( 18 wheelers). I know air systems like the back of my hand. BUT I Have to say Newell coaches have thrown me for a loop. Several people on this site will help you try to understand how it works, it can be confusing and expensive if not careful.
If you have no knowledge of how to support this coach when in the air, DO NOT GET UNDER IT..... I have 6 -20 ton jack stands , as well as 4- 20 ton air jacks  and I still get squirrly when going underneath this thing.
You stated you are in Texas, I might be of some assistance if you are close by