454cid
Sooper Pooper
NO! This is a 4.3L VIN W CPI Engine. The thermostat mounts in the front if the intake. It does not have a recessed groove that the O-Ring fits in like the '96 up, where the thermostat mounts in the top of the intake. The rubber thermostat gasket is beveled on the sides, which fits in the hole of the intake. Which I believe the paper gasket seals the thermostat housing to the intake.
Ok, found one on ebay to look at..... I forgot about that one, since it was never offered in the GMT-400.
I just watched a old video on Youtube on it, and that guy used both gaskets... not sure why on that though. Are you getting the thermostat into the groove in the middle of the rubber o-ring? That is the same as the newer engine, even if the beveled outside profile is not.