I just put a new dash insert in my sweep dash. When I went to take off the old speedometer cable I had the same problem. I went in thru the top with the dash pad removed. When I pushed in on the clip I couldn't get the cable to release. I was removing the whole dash anyways and when I pulled it forward a couple of inches it came right off. I almost think the way the cable comes up thru the dash it has some side pressure on it which makes it harder to get released.