I would contact the fitter and have a conversation - worse case you do another driver fitting.

He got you by the book, and it was the smart thing to do, that Xstiff shaft most likely had you in the fairway more.
As you mentioned T he only thing you can do is go get fit again. Number do change and to be sure it’s a necessity.
Much like checking the loft/lie on your club’s yearly. Swing pattern can change.
Let’s us know how you make out.

Too stiff of a shaft would be more shots fading right. Or suboptimal launch angle. If the numbers for launch and spin are in the optimal range and ball flight dispersion is generally straight, then you are good to go.
Shaft stiffness is not a straight relationship to head speed. Transition and feel are important as well. Shaft stiffness is not a defined feature, only a guideline. One company’s stiff may be another company’s X or even R. The TPI guys wouldn’t fit you in an extra stiff if it hurt your distance. They would have gone to a different line to solve the left pull. That’s the difference between a mass marketer with 10-20 shafts and paying for the TPI expertise and the racks upon racks of shafts to try.

Hard to say if your "left miss" would not come back after the shaft change. Tensei Black shafts are reasonably priced you you might consider just purchasing the stiff and keeping both to switch back and forth. I always like to have a back up shaft, especially when traveling in case something happens to my gamer.

great question mate, I had a similar fitting suggestion of a stiffer shaft than I usually play and was wondering the same thing

I got fitted last year on 9-24-2022 and ended up getting the TSR3 9.0 driver with the Mitsubishi Black 1k 65 gram shaft. The fitting was great, then came the season, it was my worst driving season yet. My issue that's me right now, It's definitely the archer not the arrow that's the issue. I've played TM, PXG and Titleist before picking up the TSR3. I am hoping to get this issue resolved for 2024 since driving the golf ball is one of my strengths for sure. Has anyone gone through this issue that I'm experiencing right now?

I did a Titleist fitting for a new 3 wood and also went from S flex to a project X 6.5. The issue I had with my TM 3 wood was not being able to launch high enough off the turf and not enough spin. And when I did get it up in the air the dispersion was too much both ways. At the Titleist fitting, the project X 6.5 (equivalent to XS flex) gave me a higher launch and more spin with a TSR 2 head. And it goes a lot straighter. Best 3 wood I have owned since the change to high launch low spin concept.

I always thought I was not a consistent enough ball striker to play XS. I have enough club head speed but thought the XS would not help enough on off center strikes. The new set up works well. I need to upgrade my driver and will try the Project x 6.5 also. It’s the Hzrds Black 4g shaft.