RE: So I'm getting a new bow...
Dubbya I work on bows for a living and I haven't seen too terribly many that won't tune. There is always an underlying cause. 90% of the time the issue is either in the arrow or the shooter. 10% you may have a structural issue such as a bent axle or limb twist or something else not painstakingly obvious, but certainly fatal to performance.
My advice is to honestly go with another bow... here is why.... so much of archery is confidence not just in yourself but in your equipment. It sounds to me like you are having big time regret/issues/problems with your bow, and that itself is enough to make performance suffer.
I'd CALL Bowtech (not pro-staffers but the actual company in Oregon who designs and makes the things) and bounce ideas around with them. They may well have seen something like this before, or heck maybe they will want to look at it and will give you an RA so they can give it a once over (for the price they had better). The first Marquis that came through our shop this year was a lemon... and no matter what company you are dealing with... you will see a Lemon from time to time... I've even seen it with Leupold scopes.... give them a ring and see what they will do for you.