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from Wikipedia...

The Chevrolet Titan 90 (and similar GMC Astro 95) were heavy-duty Class 8cabovertrucks made by General Motors between 1968 and 1988. When introduced, they replaced the GMC F-Series "Crackerbox" & featured an all-aluminum tilt-cab. Diesel engine choices included Caterpillar, Cummins and Detroit Diesel powerplants.
In 1980, both trucks were redesigned with a bigger grille, which was optional on the SS or Special Series Titan models and Astro 95 in 1978-79.
1980 was the last year for Chevrolet Semi Trucks or Big Rigs (Class 8 Heavy Duty Trucks).
The Titan 90 was introduced in 1969. In 1980 (the last year for The Titan), it was just Titan.
The GMC Astro 95 was introduced in 1968 as a 1969 model and made until 1987. In 1980, the name was just GMC Astro.

The GMC version was more common than the Chevrolet version.