I have drained the water from the bottome of my kenmore ultra wash dishwasher and checked to see if the drain was plugged. It seems to be clear. What else could be causing the dishwasher to back up?

There may be debris such as glass inside the pump assembly or the bearing is worn on the motor. If you can see any indication of a water leakage on the motor--it is usually "shot". When there is a leak--you should see either white powdery residue anywhere on the motor itself. This is dried detergent. On some motors the corrosion will be much more severe--- such as the motor frame aluminum disintegrating. There is a pretty steady history of Kenmore D/W's having that issue

Kenmore Dishwasher won't drain completely - Fix-it Forum: Home Improvement & Do It Yourself Repair Forum

When the dishwasher goes into the drain cycle, does the pump sound like it is running. Do you have an air gap?