Rough Running at 200 degrees

In Idaho it gets hot...believing it or not. 104 last Tuesday. The vette runs great until it hits an indicated 200 degrees or more. Then it runs rough at idle and slow speeds. I thought I was going to have to exit a parade a few weeks ago.

So I need some advice. Is this a common issue with these old guys?

Bubba installed a tranny cooler as you can see in the pics. I'm sure it blocks some of the cooling fins but maybe that's okay. He also installed an auxiliary fan. It works and does help...a little.

I'm tempted to use waterless coolant. Saw it on Jay Leno's Garage and Wheeler Dealers. Seems like a good idea.

Do any of you guys see anything that alarms you in these pics? Is this just normal for these cars?

How "rough" are we talking here? A slight tremble might not be anything to worry about....the plugs could be loading up at idle at that temp. Do you know what plugs you have in it? Might want to go a step colder for summer driving.
Could also be something more serious if the idle shakes the whole car like a paint shaker....
200* in 104* ambient temps isn't that bad at all, imho....especially crawling along in a parade scenario. If it cools back done to "normal" once you get moving, then I wouldn't be too concerned with the coolant temp. Make sure you have all of the foam seals around both the radiator core and the shroud.....those things are really critical to helping keep the temps down in these cars.

It's not rough...rough. Just threatening to die type rough. The seals may be an issue and I'd have never considered that. I just replaced all of the undercarriage bushings and they were total crap! So any soft part is likely to be very bad or missing.

I would be more inclined to look at the coil or other ignition parts that can be heat sensitive. The carb could also cause what your describing