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Use the VIN decoder on this site - https://chevroletforum.com/forum/vindecoder.php - for finding out where the truck was built - the first 2 digits of the VIN define the division. At this point in time GM was beginning to transition to the metric system, so it could’ve been built in the US or Canada.
As for who/where the individual components were made, I couldn’t say for sure. This was a time of transition not just for SAE to metric but also outsourcing some things (such as electronics) to other countries.
The truck was manufactured within the GM's Chevrolet-Pontiac-Canada Group. What I was able to research thus far is listed below. Trying to find out where seat, dash, and trim were made.
In 1989 ...
Final Assembly - Pontiac Michigan
Engine Assembly - GM Flint Engine Plant
Engine Castings - GM Central Casting
TH400/4L80E Transmission - GM Hydra-Matic Division
NP241C Transfer Case - New Process Gear Co.
Rear Axle and Driveshafts - Dana Corporation
Frame - A.O. Smith Co. (later Tower Automotive)
Starter & Alternator - GM Delco Remy Division
Electronics & Stereo - GM Delco Electronics Division
TBI Throttle Body - GM AC Rochester
Radiator - GM Harrison Division