Sorry to be the bearer of bad news, but I would guess that with your current record, you would have a very hard time getting into a top 30 graduate program even with an excellent PGRE score. I think you would have a hard time getting into any PhD program at all at this point.
For an example of how hard it is to get into grad school if you have a record of dropping out, see this guy
. He is not an encouraging example, although he did get into grad school again eventually at a low tier school. His publications were in high energy theory.
You have an addition barrier to overcome: you have no research experience. As you know, it is very hard to get into grad school without some kind of research experience, even if you want to do theory. That experience need not be theoretical or even physics, but you need something.
In your case you you need to a convince an admissions committee that against the odds
(1) you won't just drop out again like your first two tries at a PhD
(2) you have the perseverance to succeed at research
Your raw intelligence / physics knowledge (as measured by tests like the GRE/PGRE) are really besides the point now. You've shown that you can stick with coursework (more or less). Now you need to show that you enjoy research enough that you will still stick with it even when the doing gets tough -- as it inevitably does in the process of getting a PhD. Since you have no research experience, admissions committees have no way to access this.
So ask around and find a way to do research so that you can prove that you can stick through a research project to completion. As I said, it doesn't have to be theory research or even physics necessarily. Then you will have shown that you have a plausible chance of success in a PhD program. I would not bother studying for or taking the GRE exams at this point.