First I did the obvious: Changed the evaporator fan motor and condenser fan motor. Then I realized there was too little air flow from the freezer to the refrigerator, so I replaced the air baffle assembly. Now everything works again.
This should have been a piece of cake, but in the 48" Kitchenaid side-by-side built-in, the baffle assembly is mounted on the side wall of the refrigerator rather than the back wall as the video showed. That means the hole for the rear of the two screws holding the assembly is not directly visible; you have to use a mirror to see the bottom. The hole the screw goes into is too deep to hold the nut with your fingers. Since I didn't have a magnetic nut driver, I attached the nut to the driver socket using a dollop of rubber cement. That way the screw stayed horizontal while I felt around for the hole to screw it into. Once secure, a quick jerk broke the rubber cement. I cleaned off the screw head with a Q-tip.