Complex sentence: Few Stage 2s were ever used on the street and Buick only ever factory assembled 15 Stage 2 test units, one of which was a factory GSX test mule with 4-speed manual transmission used for speed testing.
Split into simpler sentences: Few Stage 2s were ever used on the street and Buick only ever factory assembled 15 Stage 2 test units. One of which was a factory GSX test mule with 4 speed manual transmission used for speed testing.