77 GMC Sierra Diesel 4x4 doesn't exist but I just bought one?

[aegeas]

I have just purchased a 77 GMC Sierra 4x4 diesel truck that I cannot even get VIN decoders to find. It is titled as a 77 GMC Sierra and has the appropriate TKZ VIN beginning, but even the GM manuals say there was no such truck until 1978. Is it possible this was custom ordered with this engine? It does have the original diesel dash and is obviously originally a diesel truck as all of the diesel lines are original. The VIN code digits seem to indicate that the truck was manufactured in 1976, but once again none of the manuals or VIN decoders think such a vehicle existed. So to sum up, I have a 1977 truck that was manufactured in 1976 with an option package that appears to have not been available until 1978. Anyone have any clues as to how this could happen? The truck does not appear to be stolen or rebadged and has a clear title. Purchasing parts for this thing is a bear as you never know what year to tell the autoparts store you have!


Aegeas