Re: Hello from a new GT owner with some reservations!!!
Any chance you are just referring to slight torque steer when quickly letting the clutch out on a very quick gearchange and stomping on the throttle? This would be possible, but would be very mild.
Does it happen with a normal speed gearchange and smooth but still quick throttle application? It shouldn't.
Another possibility is that the steering on the GT and all 156 based models is very quick so it is easily possible to move your hand on the steering wheel slightly when changing gear with the other hand and resulting in a self inflicted wobble at higher speeds.
It wouldn't be as noticable in other cars with slower steering, but just something obvious you can check.
I'm not a doctor - but I really do recommend braking later