The Viper is a bit of a handful. First Super Soft tires. In GT 2 you don't have to pit so often like you would in GT 3.
Lower it all the way then bring it up 3-5 clicks in front and 5-7 in the rear.
Springs to 9.0 in front. 11.5- 12.0 in back.
Stabilizers to 5 in front, 6 in rear.
Toe out to the first click in rear (positive, not negative number).
The Viper is Geared way, way too tall, Bring the auto number down in numerical value. Watch the gears. when 5th is close to 1.000 you can stop adjusting.
Limited slip Initial to 5. Accel the 30-40. Decel to approx. 1/2 of what you set Accel at (ie if Accel is 30 set decel to 15 or 16).
Hope that helps.

Plus by lowering your gear ratios Your Viper will be VERY quick, as well as having a high top-end