I have a Whirlpool dishwasher that is 2 years old. Lately the top rack of dishes aren't getting clean. I ran a packet of Glisten thru it, which didn't help. I took off the top and bottom arms to check for clogs, water ran thru them without difficulty. So I reassembled it and put 4 cups upright in the top rack, and 4 cups upright in the bottom. I ran the dishwasher for 1 minute. The bottom cups were full, and the top cups were empty. The water level is just slightly beneath the heating element. What is my next step?