In my book food intolerance would result in intense and sudden fatigue. What you are describing relates much to what I have been reading recently about the euphoria feed-back reagrding food. I have read about it into Dr.Abravanel.s book - what is utterly important is that you are listening to your body enough to be able to identify this.
I would wonder if it is not simply a mather of either your stomach being overwhelmed after a meal - do you use digestive enzymes at all?
either your stomach telling you its enough food - usually there are 20 min in between when our belly is full and when our brain registers the fact.