Aloha Joe, welcome to the forum.
I note that another post said GT was going to stop making 7595 arrows, so you may be out of luck there too. Although they're now making a 340 spine arrow, which might be about the same thing.
As to your question, at a 29+ draw length and 31+ arrow length, you're a little longer than most, which could explain why you need a stiffer arrow. Also, I've heard that bows cut past center are more forgiving of spine differences than those cut just to center. Don't know where your Grizzly fits in to this. Certainly one would think that a 5575 should work, but bare shaft testing is the best judge, in my opinion.
BYW, this part of the forum is dedicated to shooting form questions, so in the future you might get better answers to your tuning questions in PowWow (or they might move this post over there).