I notice you have a 28" draw, how long are your arrows? i had GT 5575s thatwere 27" that i was shooting from a 70lb bow.I ran into problems with them being underspined. They were approaching the 5 grain per pound threshold also.

In my opinion the 5575s are too light for <28" arrows out of 70Lb bows. Try the 7595s or a different brand