Sliced and confused

[msst8dawgs]

Ok....I have a Callaway Hyper X 10 degree driver with a grafalloy pro launch blue shaft 65g stiff shaft.  I was fitted by a local shop for the shaft.  Problem is, I slice the crap out of it.  I got out an old driver we had in the garage and took it to the course the other day.  Hit it straight and better distance.  It is a Great Big Bertha II 11 degree with a UST HTD extra stiff shaft.  I wasn't fitted for this shaft.  It just had that shaft when we bought it used.  I took the two to the shop and hit on the launch monitor and was consistently straighter and about 30 yards longer.  The confusing part is my swing speed (95-98) really isn't high enough for the extra stiff shaft, but I hit it straight.

Any thoughts?

[Ty Coop]

You hit it straighter because a stiffer shaft kicks less. If you have a stronger swing, you'll bend a less stiff shaft more. It'll actually kick at the ball earlier and more vigorously than a stiffer shaft will. Aka, stiffer shaft, less amplified misses. Odds are the x flex shaft is still pretty stiff even though it's been sitting in your garage and your swing speed isn't too low to benefit from it.

[msst8dawgs]

Well that was my thoughts too but I read several things in researching it that said stiffer shaft results in slice.  One reason I was so confused.  I really want to put that shaft in my hyper x.  Only problem is what if that doesn't work same as the big bertha II and I have to go pay to have switched back?