NV-4500 first used in 1992 or 1993 in GM pickups. It was the heavy duty 5spd. Special order request on half tons, and standard equipment ( with M/T ) on 3/4 ton up. Was available both 2 and 4wd.. what your looking for in a Chevy truck. 1992-2002 OBS ( 2001 was last year of OBS in 3/4 and 1 tons ). 5spd with a removable bell housing. if you find an aluminum case with an integral bell, that's either a 5LM-60 or an NV-3500 and you want neither of those