-2.72:1 Selec-Trac Full Time 4WD Sys-4:1 Rock-Trac HD Full Time 4WD Sys. [2.72:1 SELEC-TRAC FULL TIME 4WD SYS] OR [4:1 Rock-Trac HD Full Time 4WD Sys], [2.72:1 SELEC-TRAC FULL TIME 4WD SYS] OR [4:1 Rock-Trac HD Full Time 4WD Sys], [COMPLETE CHASSIS PARTS MODULE], [COMPLETE CHASSIS PARTS MODULE].