Do you realize how hot the combustion process is? I can assure you that 30 degrees difference in the coolant temp makes 0 difference in power or safety (under the condition that the water isn't boiling, and it won't do that till 230+). Technically, a hotter engine is more efficient, and therefore should make more power than a cooler one.
Could easily be it running out of fuel, although if it was fine on the dyno at 5500, I'd think it'd be fine on the street.
How long of a hiccup is it? Could also be the spark doing something funky. Are you able to datalog on the street? An SCT X3 will do that for ya.