On your Performa model, it is important that the water level in the tub fills to the bottom of the heater element. If it does not fill properly, you will experience poor wash action and little or no cleaning of the upper rack items. The fill is controlled by the water valve and float switch, but you are only concerned with the valve at this point. Depending on your water quality, sediment can build up inside the water valves, clogging them and reducing the fill rate. Since your dishwasher only allows 2 minutes to accomplish the fill, any clogs within the valve will diminish the amount of water let into the tub during that 2 minutes.
Sometimes you can take the valve apart and clean an internal filter screen, but generally this is not recommended, since it leaves you wide open to leaks if you don't put the valve back together properly. My advice is to replace the valve, since they are very inexpensive. Your spray arms come off quite easily and should also be cleaned by flushing them under running sink water and removing and grit or debris that you see plugging up the tiny holes in the arm. Further cleaning of the dishwasher with products such as Dishwasher Magic
will reduce buildup in the tub and help keep things running smoothly.