They gave the BOSS cars all they can take. You would be surprised how well a stick axle does on a nice smooth track. IRS will help them cover the spread and finish on the podiums more frequently. Those Z28s must be really stripped down as I bet the factory car performs better with the CC brakes and wider tires.
The amazing part for me was how fast Johnson was coming through the field. He literally started at the back of the entire field, both GS and ST cars, and ran everyone down. Less than a second separated 2nd to 5th place.