Curtis never sang this song, though it seems to mistakenly be attributed to him a lot, including on YouTube. It was done by William DeVaughn in 1974. The actual title of the song is "Be Thankful For What You Got", which includes the lyrics, "Diamond In the back, sunroof top, diggin' the scene with a gangster lean..."
Shock!...You are correct. All those years, I thought it was Mayfield.