I'm guessing this could be caused by a out of sequence issue? I'm bringing my upper body thru first instead of my lower body/hip?.
Yeah, that's spot on. Your shoulders are pulling your hips around currently. You need your hips to pull your shoulders around instead.
Trying to write a short blurb about how to accomplish that. Here it goes.
So from the back of your reachback, your shoulders are twisted all the way back. If from that position, you twist your back knee inward, such that it points your leg forward like McBeth's back leg does, your shoulders will follow your hips, without you actively trying to move your shoulders. This will pull your arm around, just because the shoulder is moving. You'll have to guide the disc to your right pec, otherwise the natural tendency from that motion will be to cause your arm to swing out like a windmill. That's basically how you can use your hips to get to the right pec position, with your shoulders still closed, such that you have their power available for the very last bit of your throw.
Note that you'll want your rear foot to be on the ball of your foot when trying to rotate it in, it also needs to be roughly perpendicular to the direction of the throw, otherwise it becomes difficult to get the hip rotation needed.