From your description, you are getting a bounce off your arrow shelf, which is one of the reasons you're getting erratic arrow flight. Until you solve this, it will mask any other problems you might have.
Part of the problem could be your shooting form. If your elbow is too high, there is a tendency for your forefinger to press down on the nock at full draw, which can cause the rebound. Your string forearm should be in line with the arrow. Or, the problem could be caused by not relaxing the back of your string hand. You should be taking a deep hook on the string, with the string in the first joint of your fingers and the tips of your fingers curled back. You should be drawing with your back muscles rather than your arm muscles. These two things will help you relax the back of your string hand.
You should move the string nock up high enough that you are sure any nock-high arrow flight is caused by the string nock position and not the arrow bouncing off the shelf. It could be 7/8" before you get there. Then, gradually lower the string nock until nock-high is minimized. You may not be able to eliminate it; don't worry about it. Some nock-high caused by a high string nock position is okay and will easily be corrected by your fletches.
Once you are sure that there is no arrow bounce, you can look for nock-left and nock-right indicating that your arrows are too weak or too stiff in spine. I wouldn't be surprised with your setup if you find that your arrows are too stiff. I generally use 3555's with a similar setup to yours. With your 5575's, you may need considerably more weight up front, possibly 145 grain tips with your 50 inserts.
Your nocks should be loose enough on the string that if an arrow is dangling on the string, it should fall off if you tap the string. Tighter than that and you may get erratic arrow flight.