Kendo33
The T300RS/GT Sport combination has been a nightmare for me. I've been all over various forums asking why my wheel did not work in GTS.
Well after some good suggestions from people on GT Planet I may be able to help you out.
1. Use PS3 Mode for the "T300RS "ALCANTAR" Ferrari wheel in GTSport. If you don't own a special edition Thrustmaster wheel base it might be a good thing.
Why? Because PD/Sony did not include any of the button functions for anything other than the regular T300RS. It seem the GT sponsored wheels like the T500RS are good to go. But any "Special" wheels like Ferrari or Ferrari XXX packages are not on the menu. This means your button functions are basically screwed completely up. More on that later.
2. If you are using the TH8-RS shifter, plug it into the wheel base. Do not plug the wheel and shifter into your PS4.
3. Insure the RED Mode light is one.
After making the setting changes to your wheel base, restart your PS4. It should do the calibration routine, you know spin left, spin right and center itself while the PS is booting.
THIS IS IMPORTANT: You know GT Sport has recognized your T300RS if it calibrates again when you start GT Sport.
As for the buttons, I would try setting them all to N/A except for the shift paddles. This way you can go in and test which buttons actually work for the special T300RS wheels. It's a sad thing, but it seems to be the only way. I would hope PD/Sony will eventually include the full range of Thrustmaster wheel models.