@rennsport -
thats strange, a poster earlier in this thread mentioned the same thing. What tool are you using to see the temp? I'm using iStat and all temps seem fine. But I think its worth apple looking into. Maybe there's a bug with the GPU temp and the OS panics and shuts down to prevent damage when its not actually that hot... of course it might also be a bug in the temp reporting tool your using...?
Edit: just on that, i'd have thought ~150F isn't very hot for a GPU anyway is it? i think a card should be fine upto atleast 80+C ~175F.
Just FYI, I had been running all weekend without a crash using "integrated" and no crash. But I'm now back at work so was forced to use discrete mode (nvidia card) again because i have an external monitor. Now I've also not crashed all day.
As Ian Kelleigh speculated above, its possible the issue is switching between cards as i'm locked on nvidia card and no crashes today... could be coincidence, but before using gfxCardStatus and allowing GPU switching i was crashing 15+ in a day.