The 1973–1987 Chevy/GMC truck line uses a conventional 13-digit VIN system. The VIN system changed three times during the course of the Squarebody truck production run.
1973–1978 VIN Designations
First Digit: Division
| C | Chevrolet |
| T | GMC |
Second Digit: Chassis Type
| C | Two-wheel-drive |
| G | Light Duty, Forward Control |
| K | Four-wheel-drive |
| P | Forward Control |
Third Digit: Engine
| Y | V-8, 454 ci, 4-barrel carburetor (P Models) |
| S | V-8, 454 ci, 4-barrel carburetor (C Models) |
| R | V-8, 400 ci, 4-barrel carburetor |
| L | V-8, 350 ci, 4-barrel carburetor |
| U | V-8, 305 ci, 2-barrel carburetor |
| T | Inline-6, 292 ci, 1-barrel carburetor |
| D | Inline-6, 250 ci, 1-barrel carburetor |
Fourth Digit: Series
| 1 | 1/2 Ton |
| 2 | 3/4 Ton |
| 3 | 1 Ton |
| 4 | Heavy Half/Big 10 |
Fifth Digit: Body Style
| 2 | Forward Control Chassis Only |
| 3 | Cab-Chassis |
| 4 | Pickup and Van |
| 5 | Panel |
| 6 | Suburban |
| 7 | Motorhome |
| 8 | Utility |
Sixth Digit: Model Year
| 3 | 1973 |
| 4 | 1974 |
| 5 | 1975 |
| 6 | 1976 |
| 7 | 1977 |
| 8 | 1978 |
Seventh Digit: Assembly Plant
| A | Lakewood |
| B | Baltimore |
| F | Flint |
| J | Janesville |
| V | GM Truck-Pontiac |
| S | St. Louis |
| U | Lordstown |
| F | Freemont |
| 1 | Oshawa |
| 3 | GMAD Detroit |
| 4 | Scarborough |
Remaining Digits
The remaining digits are a sequential serial number, unique to the truck.
1979–1980 VIN Designations
First Digit: Division
| C | Chevrolet |
| T | GMC |
Second Digit: Chassis Type
| C | Two-wheel-drive |
| K | Four-wheel-drive |
Third Digit: Engine
| D | Inline-6, 250 ci |
| L | V-8, 350 ci |
| R | V-8, 400 ci |
| T | Inline-6, 292 ci |
Fourth Digit: Series
| 1 | 1/2 Ton |
| 2 | 3/4 Ton |
| 3 | 1 Ton |
| 4 | Heavy Half/Big 10 |
Fifth Digit: Body Type
| 3 | Cab-Chassis |
| 4 | Pickup |
Sixth Digit: Model Year
| 9 | 1979 |
| A | 1980 |
Seventh Digit: Assembly Plant
| A | GMAD-Lakewood |
| B | GMAD-Baltimore |
| D | GMAD-Doraville |
| F | Chevrolet-Flint |
| J | GMAD-Janesville |
| K | GMAD-Leeds |
