I believe you are confusing pressure with flow. The PSI (pressure) is governed by the supply line pressure in both the hot and cold. Realize that when you draw hot water, it is replaced in the tank by an equal amount of cold water. It is this incoming water that forces the hot water out of the tank. Flow is another matter. For instance, if you have galvanized pipes, the inside of the hot water pipe may be corroded to the size of a pencil. In that situation, the flow would be very low, but the pressure would be the same as if the pipe was unobstructed. Perhaps you have a shutoff valve in that is not fully open. Another possibility is if your heater was connected with flex tubing, perhaps the hot side was kinked. You should also check the aerators in the kitchen faucet. Debris could have been knocked loose during the installation. 50 PSI is ample pressure for a house.