I don't have much else to add, but it's possible someone cross-threaded the stud if the turbos have been removed. Or it could just be galling. Either way, it sucks dealing with this stuff. I'd probably use an easy-out to get a good bite on it, then use the torch and try to break it free.
If all else fails, there might be some thread repair specialists in your area. We have a mobile guy whose business is called "Hole Works". He deals strictly with seized/broken bolts, damaged threads, etc. I've seen him work some micacles. Might cost you a few hundred bucks, but could be the best option if you aren't experienced with this stuff.