Since this is not your primary vehicle I would guess it maybe does a lot of short hops. Maybe even started and moved around in the driveway? More frequent runs where the engine sees full operating temp can help alleviate some of the build up. The flaking you see are some of the deposits coming off as the plugs warm up. I don't see any broken ceramic. I would suggest one heat range hotter if the vehicle use won't be changing any. If you won't be using the truck for the winter you'd be better off not starting it at all.
