I know you've posted this question in several places. On the page for Rocky's truck http://www.imcdb.org/vehicle.php?id=283992 you asked about a brown and gold '77 being used on the show. I replied that "I think it's always been red and grey. I think Jim's car and Rocky's truck were updated every season/year, but they were always the same color."

I've been doing the show and adding episodes in chronological order. Currently, I am halfway through Season 2, which aired from Sep. 1975 to Mar. 1976. 1977 vehicles won't show up until the end of Season 3 or the beginning of Season 4.