Dual evap so I don't think we have a problem with the dampers....this dual evap style GE has plagued me and quite a few others. Many parts have been thrown at it to no avail. There has been one almost-common symptom that we should look at...that is the condensation on the lower left side....here is a bulletin regarding ice ball issue found in some dual evap fridges. This bulletin does not specifically list your model but it may be helpful. First, however, I would replace all thermistors, regardless of the design....okay back to the bulletin. Pertinent part reads:
"Dual Evaporator models, by design, create a high humidity environment in the fresh food section. Although this design improves the preservation of certain refrigerated foods, the potential exists in some units for an ice ball to form in the lower section of the compartment due to excessively cold temperatures and high humidity. The low temperatures are created by gaps around the beverage center duct and along the left side of the Custom Cool air handler cover. These locations can be sealed and the temperature improved using the service kit WR49X10180 (120V heater) or WR49X10175 (220V heater). Refer to the attached kit instructions for the proper repair method"
So I am developing a theory that may or may not be anywhere accurate but it is something to consider. If, as described in the iceball bulletin, gaps can develop around the beverage center duct causing the left side to become too cold, is it possible that this cold area could bias any nearby thermistors causing the ff section not to cool or even defrost more than it should?
then again you could simply have a bad board. lol