Can you post the model number please.
Also do you tend to find its more the top basket?
Ok what happens a lot on these is the washer in a plastic nut wears so what happens when you push the top basket back in the top spray arms doesn't sit into the water feed tube correctly so when it pushes the water around it doesn't go fully through the top spray arm so what happens is you get poor wash results just like you have now.
What you need to do is pull the top basket out and look inside the dishwasher at the back and you will see the water tubes. You will see a round plastic nut which the top spray arm pushes into. Unscrew this and you will find the washer has worn and failed so you need to replace that nut.
Then you will find this will be back to normal again from there.
If you need anymore info just get back to me.