just run a cycle with vinegar then add again before the rinse... Are you sure no one just changed a setting on the DW??? there is a heater inside the DW and can be set on or off through settings... I be true,,,new DW/Appliances have so many settings it is confusing to me... Maybe the help screwed with it??? I do not think your WH is going bad...

This is a stretch but do you have a thermometer that goes above 180 like a probe for a roast??? test the temp of the water before you go to the garage... put the thermometer in a glass and run the hot water in the glass for like 10 minutes and see what you go up to...

Inherently a WH will get colder as it goes... it may get hotter briefly before it goes because a heating coil may short and get hot,then quickly die,,,No Where close to the time you are having the Prob,,,3 Months???

Now Dr.Bg,,,go take it's temprature...