340's would be way stiff with that weight bow and point weight.Fletching hides a lot of tuning flaws but it sounds like the matted down fletching,is losing it's steering ability and the tuning problem is showing itself.For my setups with a bow 52-55#,I need 400 grs,point and insert weight combined.At 45 # you would need more than that and would end up with an arrow way heavier than would be practical.
If you want a heavy arrow,I would try a 400 with app 250 grs on the front end but tune from there.Every setup is different.