Motorcycle with driver

The last few weeks, I've started to work on hitting a draw with my driver. Prior to that, I had been mostly hitting a slight fade with decent distance, but sometimes I found myself getting the path way too much outside-in and slicing drives, and losing distance. So I went back to basics, started focusing on the motorcycle move at the top of the backswing and getting my path more inside to out. On the range, I began to see an immediate change in ball flight and contact quality with good swings: lower flight, slight push with a nice draw. Bad swings I think were what I should expect with the changes I was making: some smother hooks, some heel shots when early extending into the ball, some big high pushes when the face was left open. After a few weeks of practice and integrating it onto the course, here's what I'm finding:

-- I can perform this swing pretty consistently if I use a shorter backswing and try to swing without adding power with my arms/shoulders. I have to feel like I'm swinging at 60% power.
-- If I try to take a longer backswing and/or add power with my arms/shoulders, it usually results in a big high push with a slight fade at the end.

My self-diagnosis here is that when I try to add power, I'm losing the motorcycle move as I come into the ball and I'm leaving the face open, because the path is starting on the correct line but it's fading instead of drawing. Based on what I'm describing, does that seem like the right diagnosis? Also, what do you recommend I should train from here? My current thinking and game plan is to just keep working and training this swing with motorcycle, a shorter backswing and less power, because I like the ball flight, contact and even distance is good. It just feels weird that I am dialing it back to what feels like 60% power to be able to hit it properly. Or perhaps I was powering the swing all wrong before (too much arms/shoulders)? Does adding power the wrong way make it harder to hold the motorcycle?