Here are your parts
Replacement parts for MAYTAG DWU9922AAM Dishwasher - Undercounter | AppliancePartsPros.com

Here is a manual
http://www.servicematters.com/maytag_library/docs/16008243.pdf

Could be a number of things.

Clean/check the filters in the unit, you may have restricted pump flow.

Next would be the unit is not getting enough water.
Most units fill to just under the heating element.
If it seems low, add a couple quarts of hot water after it fills.
Just be careful that it does not overfill.
If it now runs OK then it is probably the filter screen on the input side of the water inlet valve is partially clogged.
Remove the valve from the unit and clean/check the screen.
Do not permanently remove it from the valve as it is there to keep crud out of the valve which could hold the valve open and cause a flood.

Note: That with either of the above I would expect that you would also see poor wash results with the liquid detergent.

Next would be that the water is not hot enough.
Could be a blown heater or a bad limit thermostat.
Unplug them and check them with a meter.
Element is usually around 20 ohms, thermostat should be 0 ohms.
May also be the temp selector or timer itself.

Could also be that this unit just does not like tablets and has problems dissolving them.
In my opinion the best detergent is still the granules/powder, then liquid and the tablets would be at the bottom of the list.