Found some info;
"There were some other less common trim packages which overlapped those noted above.* They included the Z77 Chevy Sport/GMC Street Coupe exterior graphics packages that exclusively used the Z62 trim interior appointments with the addition of the floor carpeting and the V22 Deluxe front appearance option, and the BC2 Deluxe instrument cluster.* The Z77 option, which also included N67 Rally wheels as standard, was available only on the 1976 to 1981 Chevy/GMC short bed 1/2 ton pickups.* GMC offered some other interesting limited edition models during the 1975 to 1987 time frame, but I won't get into those here."
from here
http://http://www.73-87.com/7387info/7387trimlev.htm