Aging Kenmore Ultra Wash Dishwasher Model 665.13269K114

My Kenmore Ultra Wash Dishwasher (Model 665.13269K114) seems to have a mind of its own. Sometimes it cleans the dishes well and sometimes it doesn't seem to clean them at all. Typically, I throw the Cascade pod into the dishwasher. I've heard both sides about using the detergent door to protect the pod from the first cycle, which is a rinse cycle. When I throw the pod in, I'll sometimes find it partially dissolved near the door. I clean the filters often, and run the sink water to ensure 120 degree water is being used. And I typically run this cycle sequence: Smart Wash/High Temp/Sani Rinse/Heated Dry. I have done a number of resets on the unit using the "Press Pots & Pans/Normal Wash/One Hour Wash times 3/Latch Door." I have also reset the circuit breaker, which effects the same reset of the unit. My guess (based on the 5/13 date on the back of the Use & Care Guide) is that this unit was manufactured in 2013. I also called Sears Customer Service, but they could not tell me when the unit was manufactured. We bought the unit new (probably around that time). I have opened the door after it starts just to check to ensure water is pumping into the unit, and I also have steam coming out when I open the door. And the heating element is obviously working. Sometimes, during cycle pauses, I put my ear against the door and I can hear what sounds like a relay or something electronic clicking. Yesterday, I ran the unit through THREE "Normal Wash/High Temp/Sani Rinse Heated Dry" cycles, and after each time it finished, there was still evidence of grime on the dishes. Just the other day, the unit cleaned the dishes very well. Is it time to shop for a new dishwasher? Thanks in advance for your help.