Do i need a new air dryer?

[tree98]

and the while we're on the subject of this truck.... Something seems up with brakes, new drums and shoes,the chambers, slacks and s- cams/ bushings all good. The brakes work and the truck stops but it just seems like you have to step on the pedal a lot harder than you used to have to. Is there a way I can check the air pressure to the chambers ? or what else should i check? It's been like this for about a year