I will try UAC, although I already have it enabled. I'd echo the experiences of others that these issues began after 5.2 and never before. I've done a reinstall, though I will try installing it on C Drive. The odd thing is how unsolicited it is:

1) I was able to play through a lot of maps and the fairy dungeon with the gates from the Zonurskin maps. Lots of action, the perfect opportunity for a crash because of GPU heat. It never crashed. Hours later when I went to Rak'Tika and teleported to the central aetherite I had a crash. Then I have rejoined and it's no problems so far for about a minute. So it should not be hardware overheating.

I'll try that old launcher, though in my case it's been randomly ingame rather than at launch.