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Replacement parts for General Electric GSD2600G02WW Dishwasher | AppliancePartsPros.com

Remove the sump cover (Item 506 is Section 2), center inside the tub.
Check it for debris or something wrapped around the chopper.
Be careful as there is often glass in the sump.
Also take note how the inside piece goes, reinstall it incorrectly and the chopper will eat it.

Is it draining correctly?
Usually they leave a quarter inch of water at the lowest point in the tub.

Check that the unit is hooked up correctly.
Make sure you have the hose looped higher than where it enters the drain.

I do not know if this is a new problem or it has always been like this or the house pluming has changed so am trying to hit all points.
Here is an install sheet that may help.
http://products.geappliances.com/MarketingObjectRetrieval/Dispatcher?RequestType=PDF&Name=31-30515.pdf

Have you changed detergent recently?
If you have sulfur in the water it can react with some detergents.
Powdered detergents are still the best.

Once you find the cause, you could try a cup or two of vinegar during a wash (npo dishes) to see if the smell will clear.