Secondary air tank will not go past 30 psi

Was this problem there before you changed the dryer? Double check your lines to make sure they are connected in the right place.
Does the dryer bolt directly to the secondary air tank? If so I would check that connection for leaks.
Each tank has a safety valve which may be leaking. Use your hand or soapy water and check for a leak.
Each tank should have a one-way check valve at the inlet. You could swap that with the one on the primary tank and see what happens.
Make sure the drain on the tank is not leaking.
You may have a bad air leak not allowing the pressure to build.
Least likely would be a bad air gauge or wiring to the gauge from the tank.

 

Not sure if Western Star uses similar tanks to Freightliner, they are a very similar truck though. Our Freightliner triaxle we had a similar issue, and it was because a bit of engineering genius put a check valve INSIDE the air tank in the primary to secondary baffle.Cheap easy way to see if that is the problem will be to run an air line from a port in the front of the tank to a port in the back. Fixed ours! Does your gear splitter still work?