i think they had to. between that, and using double overdrive(when they went to the 6 speed) i think was the only way they could get them to miss getting a guzzler tax.
The funny thing was, the V8 firebirds and Corvettes are actually pretty efficient if you drive them normally. The sticker numbers leading to the CAGS are based on a throttle profile that has nothing to do with daily driving. With the CAGS disabled, both my Dad's Z06 and my Trans-Am would get around 30mpg on the freeway and no worse than 16-18 around town, not much worse than many "respectable" V6 sedans and certainly better than my G8 GT which did not face a gas guzzler tax.
The G8 GTX did get whacked with the gas guzzler tax but I think that was mostly because they used a lower rear-end gear ratio which just killed what was already mediocre fuel efficiency at cruise. Put in a tall overdrive gear and spend a little time optimizing airflow around the G8 and it would probably get at least 4-6 more mpg. At least, it *should*, based on the tires, motor, and drivetrain in use. Heck, a simple computer tune is worth 2-3 more mpg in the G8 GT, and the engine bay and underbody are completely wide open to generate turbulence. So a little care on the aero details should really help.
That, and putting the chassis on a diet. The Zeta platform is at least 400lbs overweight due to not using high strength steel or other lighter components. It kept the price down compared to similar competing sedans but 4100+ lbs is porky even for a large V8 powered 4-door sedan. If they do it "right", the chebby SS should be a much more mature car with improvements across the board including better fuel efficiency with the same V8 and drivetrain. But it needs an overdrive gear, some underbody and underhood aero cleanup, and the updated zeta II chassis to compare favorably to other competitor sedans.
