Here are your parts
Replacement parts for GSD4000J00EEE models | AppliancePartsPros.comThe upper spray arm is Item 570 in Section 2.
If you click on it's picture more views will open.
If you view the part from the top you can see that it is held to the roof of the tub with 2 screws so you have to pull the dishwasher to remove the arm.
Unless the arm holes are clogged with something hard you should not have to remove the arm.
If they are clogged with food particles. Run the washer for a couple minutes to soften the clogs and then pull them out with a pair of tweezers. Do this several times to get all the gunk out.
If the arm holes are clear and it spins easily by hand then it is not your problem.
Probably a filter problem causing low pressure.
Remove the sump cover and check inside for debris or something wrapped around the chopper. Take note how the insert under the sump cover is installed. Re-install it wrong and the chopper will eat it. Also be careful when checking the sump as there is often broken glass in it.
The following may be helpful.
31-3280 Clean Design Electro-Mechanical GE Dishwasher Service Manual - ApplianceDigest.comYou will have to join the site to get the manual.
Another common problem is the unit not filling with enough water.
Most units fill to just under the heating element.
This can be checked by adding a couple quarts of water after each fill during a cycle. If it now washes OK then check the fill valve.
Just be careful to not overfill it.
Often if the fill is low you will also hear a growling sound because the pump will cavitate (suck in air).
The most common cause is a dirty screen filter on the input side of the fill calve. Remove the valve from the unit and clean/check the filter.
Do not permanently remove it from the valve as it is there to keep crud out of the valve which could hold it open and cause a flood.
