Dishes on lower rack are not getting very clean,

Check the water intake screen for sediment. Sometimes if sediment partially clogs the screen, the water pressure is lowered significantly enough to cause these conditions.
If you send me the make & model of your DW I'll tell you where the intake screen is. Sometimes its on the bottom which is a pain because you have to pull the DW out of the cabinetry...

You need a new water inlet valve. They are easy to replace. Just make sure the water and electrical supplies to the dishwasher are shut off before replacing the valve which is normally located in the lower left front corner behind the access panel.