That arrow should be fine; put a square on there and make sure your nock is at least 1/4" above the center mark on the square, or even 5/16".
Those rebels do weigh about 10+ gr/inch, right?
Otherwise, check limb tiller...top limb should be 1/4 to 3/8" positive over the bottom.
Also, check nock fit; it it's way too tight, all tuning bets are off! And if you're using standard carbon nocks, it probably is too tight...try switching to easton super 3d nocks with the larger throat...
pm me if more info needed...
marc