First, you must know the difference between pressure and flow. Pressure does not change with pipe size. A 1" pipe and a 1/4" pipe coming from the same source will have exactly the same pressure. Obviously there will be more flow from the 1" pipe than from the 1/4" pipe. Increasing the pressure will increase the flow to be sure, but that's not your problem. You can buy a pressure gauge at a hardware store for under $15 and check it. I believe your flow is restricted. It could be from a valve that is not completely open, it could be from a corroded galvanized pipe, but it is most likely the CPVC pipe. The inside of a 3/4" CPVC is close to the same size as a 1/2" copper. If you insist that you want CPVC in your home, you should size it larger than pipes of other material.