Also wanted to mention that thefirst thing that came to mind was that the belt had slipped and was loose again, but I have double checked the belt and it is tight as it can be, tensioner is functioning and everything appears to be turning, so I think we can rule that out Bob. I wish it was that, at least I know how to fix that!!! I can get down to the tensioner and have it off along with everything else in 45 minutes at this point, I had to do it so much the last time the car went screwy on me.

I did notice something odd though, when I double checked the belt. My fan shroud is missing. I have no idea how/why/when this happened, I'm thinking that it was left off during one of the repairs and somehow vanished. Obviously, I need a new one, but I am loathe to think that a missing fan shroud would cause overheating to the extent that I am experiencing. Could I be wrong?

 

I doubt the fan shroud would make that much of a difference.

Let's recap ( even though you've already mentioned covering some of these) for possible problem areas:
-thermostat
-rad cap
-radiator
-water pump
-fan/fan clutch
-aux. fan
-aux. water pump ( electric pump on pass. side )
-collapsed hoses or other blockages
-air in cooling system/system not pressurized
-coolant temperature sensor
-faulty cluster temperaturegauge