Brian,
It sounds to me like the controller is being overheated and you need more air circulation around the internals of the controller.
Is the controller electronic by any chance?.
Or have a micro-processor chip?.
The Surge Diverter is a darn good start, voltage surges before and after outages can cause all sorts of havoc with electronic equipment.
The installation of a downstream contactor is also a good idea, as the controller will only be carrying the control circuit current, just keep the contactor away from the controller to prevent any problems with stray magnetic fields.
Hope this helps!. [Linked Image]