I would venture to guess that you have very strong arms and hands...and you use them too much...to your own detriment.

I would also guess that for you to hit the ball farther, that you swing even harder with them. "Speed Stick at 115-118 mph"

What you are missing is max acceleration point at the point of impact.

The speed stick does not calculate acceleration, only it's maximum velocity at some point. So, without acceleration through the ball and at it's maximum at impact, you can have all the swing speed power you want, but without out it timed correctly someone with a lessor velocity but greater acceleration at the point of impact will out drive you.

And to make it worse, they look like they are swinging with less effort...

My suggestion:

Re-approach the swing from a different angle. Start to relax a bit. Allow the body to synchronize with the arms and hands. Allow the club head to be felt, and not just the club shaft it's self. i.e. Don't just swing the club, but swing the head. This creates a different sensation. One that lets you relax the whole body, arms and hands and lets them be a sequence of simple movements that create a snap or whip of the head through the ball.

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I'm a golfaholic, no question about that. Counseling wouldn't help me. They'd have to put me in prison, and then I'd talk the warden into building a hole or two and teach him how to play. ~Lee Trevino