Starting in 1997, Corvette transmissions have had weird limitations in order to avoid the gas guzzler tax.
The 1997 Corvette was rated by the EPA for 18/25 mpg with an automatic transmission or 19/28 with a manual. Why so high? Because of both the light weight and a computer that forced the transmission to shift direct from first to fourth under certain circumstances. Thusly, the dreaded gas guzzler tax was avoided.