Diagnosis
Hard water scale is clogging the rinse aid dispenser or the final rinse spray isn't hitting. The gritty feel is dissolved minerals re-depositing.
How to Fix It
First, ensure rinse aid is full and the dispenser dial is set to level 4 or higher. Manually open the dispenser door during a cycle to confirm it opens. Then, run a cleaning cycle with a dishwasher cleaner like Affresh. Use the Sani Rinse option if your model has it for hotter water.
If That Didn't Work
Check the wash arm and filter. Remove the lower wash arm and the cylindrical filter assembly. Soak them in vinegar to dissolve scale. A clogged filter reduces water flow, preventing proper rinsing.
Heads Up
Do not use liquid rinse aid in the dispenser designed for solid/gel rinse aid. It can leak and damage the dispenser mechanism. Use only Jet-Dry or equivalent.