[todwic]

Are you absolutely sure you have compression? Or do you assume because it starts right off that compression is good? Unplug your 0₂ sensor and see if your engine changes drastically. Unplug your injectors 1 at a time and see if one cyl. doesn't change less than the others. If you have done a comp. check, what are the #'s? Do they change when its warm? Take your aux air valve off and toss it in the freezer. Does it close most of the way when cold cold (couple hours in freezer)? Change out you NPT II sensor. They're cheap and could it hurt to have a spare? I'm glad I did. Do you have a multi meter with RPM capability? Carry it with and when it doesn't start, hook it up and see if you have secondary ign pulse.
IT IS BAD TO RUN YOUR ENGINE IN THE HOT ZONE FOR EVEN JUST A LITTLE WHILE. I'll say it again because it bears repeating. These aluminum heads and blocks WILL NOT take operation in the yellow area of temp gauge. My opinion is that you either shot your head gasket or warped your head.