Some dishwashers will conceal black sludge in the front of the floor, in back of where the door lowers. You can only see it if you stick your head into the dishwasher and look down. Check to see if this is true with your unit. Kenmore Elites have (had)this issue.
Some of them have an easily removable gasket along the bottom edge that the door closes against, and some just have removeable corners. Pull it/them out and clean them too.
Wash an empty load with a small amount of regular dw detergent and a cup of vinegar.
We add a lemon slice (squeezed already on the fish I caught- lol) on a fork in a wash once a week and use our own dish detergent of washing soda, Borax and baking soda... no chemicals.
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