I'm sure someone who really knows what's up will blow my post away but this is what I've done. Also if you have not already bought all the upgrades you might really want to wait for someone else to post. This car was my guinea pig.
I was surprised that this car was as squirrely as it was at first too so I threw a ton of money at the problem. First off I've bought all the top upgrades. I mean everything with the soft racing tires, all weight reduction and stiffening, engine upgrades, intake, muffler, drivetrain stuff (with the Torque Sensing Center Differential , not the LSD), the works.
For control though, the fully custom suspension and tranny really helped immensely. I also put the better rims and ALL the aero kits on it so yea I spent some cash heh. Then for the tuning:
I lowered the car by maybe 5mm in both the front and back. I stiffened the springs by .5 in both the front and back, and then upped both dampers from 5 to 6. I upped traction control from 5 to 6 and increased the number on the ABS breaks from 1 to 3. Very small adjustments there. Skid control is turned off for me. I didn't modify the wing at all. For the tranny then I either guess my top speed for the track or hit a practice track to see what the top speed on the course is and set my tranny top speed to just above what the car can do on the track.
Anyway all this helped the control a LOT. I'm sure there are much better ways especially if you do not want all the upgrades but what I did definitely made a huge improvement. It went from me not wanting to use it to loving it. Learned a ton to apply to other cars too. Like I said though this is pretty much me just going in and playing with stuff. It's still a work in progress, but I got this thing smokin & cornering now.