Yea - doesnt sound like a servo/BEC issue. You can usually recreate those on the bench.
I'm not too smart on those ESC's, but if it has a limit of 7.5T (that being the lower limit), I think the castle falls below that? I'm not sure what its rated in turns, but @ 3800kv, I'd GUESS....5.5T? Not sure with it being a 4 pole, how that figures in. Its a neu style I believe, so I dont think it follows the turns conventional motors are given...
My money would be on the ESC. How are temps when you come off?