When I try to slow down and let the hip shift start the downswing I get severly underplane. I drop my right hand and shoulder at the same time.
From your vids, the impression I get is that your hips and shoulders rotate in unison in the downswing, giving the appearance of a 'shoveling' effect to your swing. Once you get to the top of your backswing and establish your hip-shoulder X-factor, your hips should have begun their shift and 'stretching' out the angular difference between your hips and shoulders. Do you feel your hips and shoulder moving in lockstep into the downswing and you are forced to vigorously sling your arms to complete the swing? This may keep you on plane.
When you slow your backswing to give your hips time to shift and start torquing for the kinetic chain, that upsets your core action resulting in the right hand and shoulder dropping. In effect you get 'disconnected' in your core between the hips and shoulders. The timing of the kinetic sequencing is also disrupted.
Suggestions? Suck in your gut and tense your abs because you may be going lax. Now try it again and see if that reconnects you. It's all conscious action, so it might not result in good Impact, but at least you will have a 'feel' of what your body is doing. Good luck!
If your asking if I have a large chest, yes I do. My chest is wide as well and I think it causes alot of my swing issues. I really consciously have to turn it back and through cuz it definitley wont move without momentum. Any suggestions?
Don't attempt to backswing to club parallel at the top .. just go 3/4 or 7/8ths at most. When you feel your left upper arm pressing heavily on your pec, your backswing is complete, so don't try to raise your arms any further. From there your broad shoulders can lash the arm-club assembly with abandon. Trying to stretch too far up and back is not for you!
You do sound like you are struggling with your powerful build and trying to swing like somebody who is slim with a lot of core flexibility. Have you identified your optimal swing style according to The LAWs of the Golf Swing ... because you may be attempting the wrong swinging style action?
Please remember, I am making these suggestions based only on viewing your 2D vids and your comments. I don't teach, but I pride myself on sensing the golfswing kinetic chain .. something golf instructors are unable to do ... it's a special talent requiring an appreciation of Newtonian physics ..