Engine shuddering at low speeds with A/C on; intermittent red triangle/VSC warning lights

2008 Gen 2 Prius, 177k miles

1) Red Triangle - Master Warning Light
2) Orange (Symbol)CHECK - Malfunction Indicator Lamp
3) Orange (!) - Brake Warning Light (but it didn't highlight the word 'Brake' in red)
4) Orange VSC - Vehicle Stability Control Warning Light

On the Screen:
Orange Car w/ the ! symbol - Hybrid System Warning Light

This has been an intermittent issue; when all the warning lights turn on the ICE engine turns completely off, leaving the vehicle under battery power leaving me less than a mile to find a place to pull over. When I shut the car off and turn it back on the ICE engine starts again, and all warning lights except for the Red Triangle turn off, whole the Orange Car with the ! symbol stay on. They eventually go away.

I've noticed this tends to occur during the day time at low speeds with the A/C on, and also while it's really hot outside. I recently changed the oil, transaxle fluid, and inverter coolant within the last 5k miles. The ICE coolant has 100k miles on it (that's right, one hundred thousand; I'm changing it soon). 12V is good and was replaced last October. Inverter pump was replaced between 50k-75k miles. No strange or unusual noises, just the shuddering/vibrations at low speeds. I have a code reader but need to get Windows XP installed on an old laptop first in order to run the ancient software. MPGs have not been affected.

Searched around and haven't quite found someone with the same issue.

 

1. Engine oil level is good; just changed it and checked it yesterday.
2. Coolant has turbulence in it
3. Hybrid battery seems fine; what are the basic checks? And if there was something wrong with the hybrid battery, why would the ICE be forced to shut down leaving me on electrical power only?

 

ICE coolant is full; it just needs to be replaced since it's at 100k. I'm thinking a possible engine misfire at certain RPMs or something weird with the A/C compressor. Not quite sure how it relates to the ICE engine shutting off along with the shuddering, as it tends to do that when the car first starts up at low speeds. I'm also not up to speed on how the A/C system integrates with the ICE engine.

Interestingly enough, I did see TWO Gen II Prii broken down on the side of the road today; it was 91 degrees outside today.

The car no longer has the warning lights at this time, but I'd like to figure out what's going on. It seems like if I gun the engine the shuddering stops, so it may be an RPM range that triggers this.