Hi, James.
First adjust the freezer temp to warmer setting. Give it 12hrs and check freezer temperature. See if that make a difference in the refrigerator side.
If at let say 0*F in the freezer it still be freezing produce in the fresh food then replace the damper thermostat #21
Part number: 240383703 
Use the old insulation tube.
Here are the breakdown diagram and
Controls replacement parts for Frigidaire FRS23BH6CS0 Frigidaire/refrigerator | AppliancePartsPros.com
Thank you. Post the results.
Simon.