I have noticed that my hip rotation stops before I get to impact and I slide forward more to the target from that point in my downswing. Could this be the cause of my swing path from the outside?
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Have you noticed this on video or is this something you feel is occurring?
Generally if your swing is "across the ball" you probably aren't "sliding" enough.
It can be the cause but what's the cause of your hips stopping to rotate?
Can be physical - they just don't move well...a simple hip rotation test will sort that out and you can do it yourself with a 6 and 7 iron. TPI's self-test (lower quarter rotation) is a free starting point for you and you'll have a decent answer in 15 minutes.
It can also be mental - if your goal is the ball then the brain will initiate movement to there and stop caring after that. That's a great recipe for the body to stop. If the body stops and the arms keep going the only way to not hit yourself (self-preservation) is over-the-top. This has been showing time and again with club-throwing drills or other target focus tips.
I'd look at both possibilities and yes a great idea to post vids.