Never had it slip unless I was riding my foot close to the pedal. Even a very little pressure on the pedal between shifts is enough to cause it to lift off some pressure and then it might slip.
My wife did that just last night and because she was being lazy she didn't lift off fully before she nailed the pedal in second gear. Funny, it was because this guy in a Dodge RT 5.9L (I think that was the size.) took off. She just stayed with him up to the speed limit.
Actually she did everything wrong, I was pissed.
She takes off tires spinning out then its just bouncing off the rev limiter like four times before she shifts. I was just starting to say something. Then she nails it in second and I can hear it start to slip and then she lets out all the way and it takes off.
LoL! I was too busy laughing at the dude in that truck to pay attention to all that she was doing wrong.

Afterwards I explained that same fact to here that I explained to you.
Anyway, the pucks are sintered bronze apparently. There may not be anything wrong with it but I'm not sure what it will do when it is getting close to its limit.
Mine have always worn similar to a stock clutch.
Still, with those temps and a hot bottle, you were probably pushing 400 ft-lbs. Hell, I push close probably 350 ft-lbs at the flywheel. You're running a serious shot on an engine that is really efficient with nitrous. You just might have been getting close to exceeding the limits of grip.
Still, I'd check to see if you just weren't letting off on the clutch pedal all the way first.