Switched to a 65g TP club/shaft - Can't stop hitting shots left and right

I used to play a Cleveland Hi Bore XL with a 55g Regular flex shaft. I won a few company tournaments with it and never lost a longest drive contest. Even though this was the case, it never, ever felt good in my hands and I never was able to hit it consistently.

I recently went to Golf Galaxy and tried 4 different Taylormade drivers. I ended up falling in love with the R11s. The pro noticed that my club head speed with the driver was averaging 105mph and my ball speed combined was perfect for a stiff shaft. Lucky for me they had an R11s with a Stiff flex TP (65g) shaft. I was extremely excited that I finally could generate the club head speed to move to a stiff shaft, but I quickly found out why the flex of a shaft matters haha. I played a few times with it and more often than not I notice that I am slicing the ball. The ball appears to go straight and long but then all of a sudden takes a sharp right turn and ends up with a slice. I'm not sure what could be causing this.

I was at the US Open this weekend and Phil Mickelson's trainer gave me a few pointers on how to fix my swing. Though it helped, I'm still a bit more inconsistent than I want to. On the other hand, I play the Rocketbladez Tour irons with a regular flex and I'm able to hit them so well. I have been able to shape my shots when I want to with my irons. I just don't understand why I can't hit my driver now.

Any help would be greatly appreciated.

Do you know if the clubface of your new driver is closed or square?

They made 2 types of your old driver. A tour model which had a 3 deg open face and a regular model with a closed clubface(toe pointing left). You probably had the regular model with the closed clubface which makes it easier to hit straight or draw.

Your new driver may have a square clubface which is causing you to hit it right.  With your handicap you would probably benefit using a driver made with a closed clubface.

The R11s allows you to adjust the face angle. You might want to try adjusting that to closed. It probably came stock set to square.

I'm betting your old model had a closed clubface and your new is set to square.

The straight ball that then slices off the the right is because of an out to in swing path to a clubface that is square. I don't know of any reason that the stiffness of the club would be causing that, but I could be wrong.

I have about a 115 clubhead speed and only switched to a stiff shaft just 2 years ago. My old driver with a reg flex was extremely inconsistent. I had all sorts of different launch trajectories and shot shapes and I went for years without being able to fix my issues with the driver.

I finally switched to a stiff shaft (an R11s :D) but I didn't immediately start hitting it straight and long. But I did find that at least my misses were more consistent and I was finally able to diagnose what I was doing wrong and fix it and now I am very confident on the tee box.

I think that a consistent miss is a whole hell of a lot better than an inconsistent miss.