R.S.
I was having this problem with my dishwasher...we had had it over ten years and other than occasionally throwing some vinegar or other cleaning agent into it I had never cleaned it. My dishes sometimes looked worse when they came out than when they went in.
I googled the brand and model of my dishwasher and found a you tube video showing me how to clean out the filter...which if clogged could cause this issue and of course it is under all the working machinery in the whole thing. However the video showed me step by step how to disassemble the machine clean it and put it back together...all I needed was a screwdriver.
Be prepared to spend all afternoon and be about a grossed out as you can possibly be...I was surprised we hadn't caught some horrible water/bacteria or parasite from all the gross globs, caked on crud and "stuff" inside and under every part of the machine. It took two whole rolls of paper towels.
And when I finally got down into the filter...I found a couple of coins?? A. apple stem, two sippy cup valves, a huge piece of cellophane wrapper and one other thing I can't remember right now. (Or maybe I have blocked it out...)
Anyways if nothing else works...disassemble...clean...and reassemble and it will work like new.