After some research the most likely cause was identified as the fridge evaporator fan. The fan had been making some noise but seemed to be running though temperature kept rising. I ordered an exact replacement fan shipped overnight air. The how to video on fan replacement provided by this supplier is an excellent guide to the diy guys like me. Following the video directions I had the fridge disassembled to the evaporator/fan in about 45 minutes; I am very careful following instructions. The instructions in the video are clear and made the job fairly straightforward and saved me many hundreds of dollars in a service call. It helps to have a second person to hold the back panel for a few minutes while you remove the electrical plugs.
Total time from removing the first screw to inserting the last one was about 90 minutes. If I ever have to do this again I'd say time would be 30-45 minutes.