Just a quick follow up. I got both the aftercooler and air dryer rebuild kits, will get to those this week. The main issue was my aftercooler purge valve not seating back fully after the purge, and then air pressure continuing to fall. I bought a new aftercooler purge valve as well, about 30 bucks. Since it looked like the easiest fix to make, I slapped it in in about 5 minutes. I didn't have a 1" allen wrench so used a 1" nut to extract the old valve and re install the new. I packed a bit of paper towel as wadding in my socket and did the same in the valve itself otherwise the nut I used would fall in one way or the other and not have enough bite to turn the valve. It works like a champ now. For reference the part is Haldex RN60F purge valve kit for pure air.
The old valve spring seemed fine, and the two o rings were intact. The new kit comes with the proper grease and instructions call for lubing both o rings and the piston itself. The piston was clean but completely dry... its quite possible that the old valve would still work had I simply lubed it up but not taking any chances.... no fun watching air pressure continue to drop on the road, and having to exit the truck and manually push valve back in to hold pressure long enough to get home.
