That is not a GM weatherpack but it might be a Delphi metripack or similar.
Fun fact: GM's Packard Electrical Division made most of their connectors. It was spun off to become Delphi (an electrical connector maker whose products are sold on digikey, mouser, etc) and many of their molds still have the PED makers mark in them, so if you see PED molded into a connector it is almost certainly a Delphi/GM product of some sort. Some of the datasheets on their site are scanned-in original hand drawn mechanical artwork with dates and engineer signatures going back into the 40s! Many gearheads call all waterproof connectors weatherpacks, but there are dozens or even hundreds of series and only one or two are actually called weatherpacks. Most 80s and 90s vehicles have at least a few dozen Delphi MetriPacks in them, both sealed and unsealed varieties.