GE Refrigerator Cooling Problem

We have a GE Model GSS25JFMC side by side refrigerator/freezer that will just not get really cold in the refrigerator section any longer. It's one of the models with the "Smartwater" filter in the top part of the refrigerator section (which hasn't been changed in a long time, but I have an emergency cut-off in case it cracks, which it did at one time a long time ago).
Freezer keeps food cold, ice maker works fine, cold water and ice dispenser/s work fine, the little vent down at the bottom in the refrigerator section is on the coldest setting; I clean the coils and section under the refrigerator really good at least once a year, and it hasn't been 4 months since they were cleaned.
The appliance has worked fine in it's present location for a long time, and is 8 years old. This just started about 2 months ago; it keeps water and drinks cold, but at one time, we had to be really careful or these items would actually freeze.
Both settings (freezer & refrigerator) are on 9, the coldest settings. I've unplugged the appliance for about 30 minutes, to see if something needed to reset or whatever, and have changed the temp settings down to 5 or so to see if that somehow would reset something, but nothing has worked, and I'm about out of ideals. The unit is still very functional, but is just not keeping things in the refrigerator section nice and cold like it did at one time.
Any constructive comments appreciated. Thanks !