Need a little more info before we can help you out.
I run my gt2 at
Sens 700 ( 440-500 for race cars)
Ff 100. ( 80/90 race/ high downforce cars)
Spring. -3
Damp. -3
Abs vibe varies from car to car. Generally around 75%
Drift off
If you are driving straight and barely touch the wheel and take your hands off the car goes out of control. You have to hold the wheel so tight to keep the cars from getting out of shape. I don't have this issue in any other game with this wheel.
High downforce is causing this.
Try raising the deadzone on step to 10. This helped alot for me on cars with high downforce. The problem is on the way PD coded the force feed back.
Tuning the suspension helps some too. Not sure on what to change tho but noticed a big difference after using some tunes from this site.