That happened to me – dishwasher backed up a lot. At first I thought it was insufficient venting on the drain line… replaced a burp valve – not fixed. Turned out the drain line in the floor was plugged going to the main drain header. I had a plumber tear up the floor and pull it. A three inch diameter drain pipe had less than one inch opening remaining – rest was deposits and corrosion. Cost less to fix than I expected too – only about $600. I thought tearing up my basement would be a lot worse but two guys did it in about 4 hours. My basement isn’t finished so no additional cost.
Point is trace the lines – understand how the flows go – you will likely find your ‘pinch point’ after you do that.