i dont understand why people want to shoot out so far with a bow...

I like to practice out to 65 yards. Then when I move up to 30 yards I am much more accurate. For me it improves my accuracy a great deal. I dont shoot at game at 65 yards.

Same here. I practice out to 70 yards. At these further distances any errors in your shooting form/technique will be magnified. And if you can keep 5-6 arrows in a 5" or tighter group at 70 yards - at 20 and 30 yards you will be packing your arrows on top of each other.

What's your FOC?

What's your velocity leaving the bow (Not your bow's IBO speed)?

Total arrow weight?

When you say your arrows are diving past a certain range, are they actually diving, or are they becoming unstable? Those are two very different symptoms.

In general, I very rarely have found that a shop can tune my bow better than I can, and I wouldn't consider myself anything special in terms of bow-tech-ing. It's been years since I've seen a shop check cam/idler alignment, and most shops around here don't even know what tiller tuning means. A lot of folks assume that if they take it to a shop, it comes out perfectly tuned. My experience is the opposite - if I have a shop install a new set of strings, I generally know I have to fix the errors that they built into the bow.

I've also found, similarly, that most shops will recommend exactly what the spine charts recommend, which is almost ALWAYS wrong for 300fps+ bows. "You should be fine" is what I normally hear. Keeping in mind, that if you buy 400's, have a problem with spine flex, now you come back and buy 340's, they garner twice the profit... Not saying it's intentional, it very well could be inexperience or ignorance, but that has been a common complaint I have helped guys fix over the last few years since speed-bows have become so readily available and affordable.

what is your arm span. 31.5 inch draw that's pretty long you must be around 6'2" or so. you need to tune your broad heads first. go on youtube and look up how to broad head tune click on the video by Kenny parsons (bow tuning tips) excellent video and he goes into detail about how to tune. he also has an entire library of fun videos on how to do almost anything bow related

been a while since I threw in my .02
 

sounds like to me you have too weak spined arrows for your draw length/weight paper tuning will tell the tale
when you went from vanes to feathers gave me that idea you would probably get the results you were looking for with a lighter grain broadhead using the blazer vanes.
but that is just a theory since I cant examine the bow and arrows.