That 340 size may be a bit overspined. I know that most bows like the MM VFT like a stiffer spine but I am shooting the 340s with a 68 lb draw weight and a 30.5 inch draw length (100 grain point). If you can get your hands on a 400 size Beman then give it a whirl and see if it changes anything. You could also go the less expensive route and just get some heavier field points to weaken the spine of those 340s.

That is, ofcourse, if spine is the issue.