Our D is similar, as are our throws, so I'll share with you what I've been working on.
I am also prone to rotating out too soon and have been trying to drill to overcome this. There has been many a "your arm is a whip" analogy made on this site, and it may be overdone, but it's relavant here so I'll make it again, with my own twist.
When you snap someone with a towel, your hand moves twice. First, to throw the towel out in the intended direction, then again to actually snap the towel once it's almost straight. When someone cracks a whip, the handle moves twice. Once to throw the whip forward, (as the whip moves forward the handle stays still) and then again, once the whip is almost straight, to help crack the whip.
Rotating out of the throw too soon is the equivalent of turning the handle of the whip (your shoulders)in a constant circle. The whip (arm) will never crack this way because the handle pulls it to the side before it straightens out enough to crack. The shoulder needs to move twice, just like the handle on a whip.
I personally never got anything out of the right pec drill until recently, because i was starting with the shoulder. It was only after I figured out that I had to get my arm out front before the shoulder moved that it became useful to me. I have been using the backhand hammer drill to find the point where the shoulder pulls the arm to the right.
I don't know if you've tried the hammer pound drill or not or if you've had any success with it, but i suggest getting it down before doing the right pec drill, as the right pec drill should really be just adding more body movements to the hammer pound drill (you should be pounding the hammer every time you do the right pec drill). If you haven't tried it, or have with no success, i suggest trying it limp wristed at first, and letting the inertia of the disc bend your wrist back ad you swing your arm, and then feeling the disc open your wrist when your arm stops. There shouldn't be any body movement at all. If you've read that entire thread you saw Blake say that you don't want your wrist to be acted upon by the weight shift of the disc, but for your wrist to be part of the movement, I just think it's a good starting point to try it limp wristed at first.
Once you've got a good feel for it and you can feel the weight shift, and are getting some pivot around your finger, think about how much more powerful you could make that feeling, how much HEAVIER you could make the disc feel if your arm were moving to the right during the wrist extension, OPPOSING the wight shift of the disc.
This was a major "ah-hah" moment for me. Then I was ready to add some shoulder rotation/right pec drill, and am currently working on the timing of the out motion in conjunction with the wrist extension/disc pivot.
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