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.