HI! You don't give the model number of the dishwasher, but if it is an 18, as in KDS18 on through the early 20s series, there is a blue flat tube between the wash arm under the upper rack and a water feed port on the back wall of the tank. Over time, this tube softens and does not permit an adequate water supply to flow to the upper wash arm. If the dishwasher is an 18 series, it has a troublesome black bellows on the end of the water feed that goes into the opening of the tube under the top rack. If the bellows is worn or torn or the little plastic insert in the bellows is missing, that could also be a cause of of your problem. Make sure that the dishwasher fills to just under the hub of the lower wash arm and listen while the machine is on for the sounds it makes. The strong water circulation should continue through each phase of the cycle until it drains. If that sound fades or you do not hear a strong rush of water when you hear the drain valve snap open, you could have a bad or partially blocked drain valve in your machine which will let water dribble out slowly during the washes and rinses. That will reduce the cleaning a lot.
Another thing to check is the lower wash arm. Pull the lower rack out and give the arm a fast spin. If it shudders quickly to a stop and you can wiggle it up and down when holding on to the end of one of the arms, the wash arm (and probably the wash arm support) will need will need to be replaced because the poor fit is allowing water to escape underneath the wash arm hub instead of squirting up and washing dishes. The pump impeller could also be worn which would reduce the water pressure, so it needs to be checked also.
