5y11m old Kenmore Elite 665.13129k701 no longer drains properly. After a "Normal" or "One Hour" cycle, milky colored water still remains in the bottom - about 2 inches worth. Selecting "Cancel/Drain" will then drain the remaining water out, but milky spots are on everything. Then I run the "Quick Rinse" cycle and everything works great, drains great etc. No unusual noises are noted - everything sounds like it is working normally.
So far I have tried the following:
*Cleaned both filters
*Put the drain hose over in a bucket - no change in results (1+ gallons received but not all)
*Poured water into the drain hose - water did not leak into dishwasher

What is the most likely culprit? Seems odd the drain motor doesn't drain correctly in the two wash cycles we typically use, yet works when you select "Cancel/Drain" or "Quick Rinse". Trying to decide what part to buy or whether to buy new. Under 6 years is the earliest failure rate we've ever had with any appliance. Thank you.