Why would a 1990 Silverado 4x4 have an RPO code of an MY6 transmission? I'm hoping that it is an A833 trans but could it be an NV3500? I thought that the A833's weren't available after 1987.This truck has the 4.3 engine in front of the trans! I want to grab the trans for my square body 79, but something seems strange.The rpo codes are still there in the truck and even the owner's manual stating that its a 1990. I'll have to lift the truck up out of the weeds before I can do a visual.