Originally thought it was most likely a defective water valve but, based on low water output from the door dispenser, it caused me to suspect the water filter as well. This is my mother's refrigerator and I am not familiar with what is "normal" with her dispenser volume.
Ordered both parts (the water valve will fail at some point anyway) and installed the filter first. Be sure to bleed the air out by dispensing about a quart of water until air goes away.
Problem solved and I have a spare water valve when needed at a great price! Quick delivery and great prices!