In my experence....the speedo cable was harder to get off than on. To make things really easy, crawl under your truck, and disconnect the clamp that holds the cable to the frame. This will give you about a foot extra to pull through the floor, or fire wall, making more room to get your hand behind the cluster.
One more thing no one mentioned ....You have to take the cover off you steering colum to disconnect the Gear Indicator cable. BE VERY CAREFUL!!! the cable is inside a tiny plastic tube that is very brittle. If you break it, your indicator won't work properly, it can not be fixed, only replaced. The CHILTON's manual outlines this procedure step by step. If you don't have this manual, it is well worth the $24. It has saved me thousands.