Just finished a 1-hour test with the new TT (not my favorite track, but a lot of fun with this car) and the weekly race, and had zero issues.
In the end, I checked the calibration and it was perfect. I loaded the default settings and noticed it was set to a 5% deadzone at the bottom and 95% at the top instead of 0–100%. To leave a little bit of leeway, I adjusted it to 0–98%, even though it probably wasn't even necessary.
Now I can hold out for another couple of months before upgrading. I'm still on the fence about the brake, though. At first, I hated the G29's rubber stopper compared to the G27, which had full travel, but by now I’ve gotten used to it and I can trail brake exactly how I want. Then again, if I were to install the TrueBrake, I’d definitely get used to that too. It’s just a matter of whether I want to reset my muscle memory for the brake or just stick with the stock spring and rubber block setup.
As for the tires and car mods, it’s been a well-known fact for a while now that they slightly change the physics. In fact, it was actually mentioned here on the forum back then, which is how I first found out about it.
Back then, I did some testing (only tires, I never added spoilers or anything else) and, for me, the stock setup was faster. Wider and bigger wheels made the car easier to handle, but slightly slower and prone to understeer.
In my opinion, they are only useful when dealing with road cars that are very difficult to control; in those cases, fitting modified tires gives you a bit more confidence, which helps drop your lap times. However, if you learn how to handle the stock car, that's how you get the best times. Just my two cents.