[jskrdla]

Our new GE dishwasher doesn't get the dishes clean even on moderately full loads of dishes. Often the powder soap(cascade) is caked inside of the soap dispenser. At least 1/3 of the dishes need to be washed a second time as they don't get clean the first time.

[denman]

Here are your parts
Replacement parts for GLD5660V00SS models | AppliancePartsPros.com

Since it is new you do not want to mess with it too much as you do not want to void the warranty.

You may have a low fill condition.
Most units fill to just under the heating coil.
One way to check for a low fill is to add a couple quarts of hot water after each fill of a cycle. Then if the dishes wash OK it is probably a low fill problem.
Just be careful to not overfill the unit.

Also often a low fill will cause a pump to growl as it is sucking in air so if you add water and it quiets down that is also an indication of low fill.

If it turns out to be low fill:
1. Check that the hot water supply to the unit is fully open.
2. Check for any restriction or kink in your supply line. Filling is just a timed event so is dependent on the supply.
2. Remove the water inlet valve from the unit and check the input side.
Most valves have a screen filter on the input. Looking at the part's picture this one may just use small holes. In any case check that it is clean. Do n ot permanently remove it as it is there to keep crud out of the unit which can hold the valve open and cause a flood.
My thought here is that when it was installed some crud came loose from your supply line and is now partially plugging the valve's input.