Agree big-time with thepainguy on the hip rotation. I've always thought (as have others) my kids velocity would have progressed further from soph in hs to soph in college. 79-83 in hs and about 80-85 in college despite gaining about 50 lbs of muscle and bulk.
At Perfect Game showcase in Fla. during hs PG write-up noted he gets "little or no help from his backside", which was dead right. Never could get him or anyone else to see it or more importantly correct it.
After 2 years of inconsistent control & velocities he agreed to see an instructor who thought he could get thru to him and give him the "feel" of using hips and body to rotate.
Gunned him on a jugs before he saw the guy and he was 79-85. 10 days later with just the thought of incorporating the hips and getting back leg thru he's been 85-92 (stalker) with much better control.
I have no idea if his velo will stay up there or drop down as it has in the past but it's really helped his follow-thru/control, and confidence.
Point is, never give up and have a number of people look at you. Mine's back leg was not only not "getting thru" but was actually dragging and digging into the ground - almost a brake stopping his momentum & some frame by frame video caught it. Good luck to you.