Quote Originally Posted by 02BlueGT View Post
The ishs are because some of the motors between 03 and 05 are series II/III hybrids
For GPs, everything up to 03 are 100% Series II. 04+ is 100% Series III. It's other cars like Impala/Montes that still offered the "Series II" during 04 and 05 that you get the hybrids. Based off Series III engines (since Series III was being made at the time), but with some Series II components added on to keep them as a drop in component to Series II uses.