OK thanks for getting back to me. Just wanted to make sure there wasn't something else I should be checking. Don't feel like dealing with the mold inside there again.

Thanks for all the wisdom. You saved me a bunch of money. Take care :D

I removed the old piston and nut. The rubber plug was half gone. I replaced it with a new one and ran the dishwasher. I cleaned and checked all the hoses and the line into the garbage disposal. I did not find any blockages, they were clean.

There is still a small amount of water by the sump cover, not quite a 1/4 inch. Is this normal or should the tub be completely dry?

Here are your parts
Replacement parts for General Electric GSD4010Z04AA Dishwasher | AppliancePartsPros.com

Is this a problem with the main pump?
I do not think so. If the unit is doing a good job washing dishes the main pump is OK.

I had a unit like this and it always left a little water just around the sump, about a sixteenth on an inch. This is normal as these pumps do not like to run when low or out of water, it can damage the pump seals.

A 1/4 inch does seem a little too much.
The most likely culprit is the piston and nut (Item 564 in Section 1)
It is under the screen filter at the back of the tub.
It unscrews.
If it does not seal properly some of the water during a drain cycle gets back into the tub instead of going out the drain.