[brown7373]

I was just ready to post a question about the top trim level 1972 GMC when I saw your post. I was driving the other day and saw a pickup identical to mine, except it was a GMC, not a Chevy. Same color, same seat vinyl, same options, same rear slider window. So it, and yours is a Sierra Grande compared to my Cheyenne.

My slider hardly moved too. I sprayed the tracks with silicone spray, and worked it back and forth, then sprayed a little more. After a little bit, it now slides pretty well. I had looked into replacing the rubber in the channels, but at that time, I couldn't find anyone who made the right stuff. But mine works fine now, as is.