Losing air pressure when braking hard or coming to a stop.

I drive 2008 Mack Pinnacle, and when I drive in heavy traffic the brake air pressure drops down to 70 psi and the brakes lock up - until the air builds back to over 100 psi.
I have gone through multiple system checks and have not found any air leaks.
My thought process is towards the compressor - if the compressor is not producing a steady flow of air, then the system air pressure will deplete down to a level that causes the brakes to lock up.
Does anyone know what specs are to verify if the compressor is working properly?
Thanks for your help with this.