Sounds like the seals in the pump stuck together.
This is very common problem for most of dishwashers, even the most expensive.
I do not think you need to replace the motor, just install the new impeller kit. The volute seal has to be replaced too. The cost of repair is less then $30.00
The dishwasher has to be removed from the cabinet for this job. You can find the complete instructions in the tech sheets behind the bottom panel.
- The part number for the impeller kit is
AP3738238
- The part number for the volute seal is
AP3039198
Here are the break down diagrams for the Whirlpool dishwasher
Model GU1500XTLQ2
Gene.