The rope and lubricant idea is the greatest. Lay the rope in the bottom of the groove and wrap it around the perimeter overlapping the ends of the rope on the bottom edge of the glass frame. Then set it back in the Blazer top with the bottom edge first. With someones help, gently putting pressure on the glass from the outside you can be on the inside slowly pulling the one end of the rope toward you. You will see it lift the seal up and over the lip of the opening. It may take a few tries to get it but it is a good skill to have.
I have succesfully used a cotter pin removal tool many times in the past to do the same thing but mine has been dulled so that it is not sharp and end up poking through the seal.
THis is obviously for reinstalling the slider, Getting the old glass out is also fun. I use that same cotter pin tool to pull down on the inside lip of the glass as I am pushing outward and then working around the perimeter until the top and half of the sides are out, then just lift it out of the opening.
Another note here is that my 87 K5 slider windows use a rubber seal that has a "Lock Bead" to seal it once the window is in the truck top. You will have less trouble with that type of seal if you can get it from the slider window source. Sears and auto parts stores sell the "Lock Bead" tool to reinstall the "lock Bead".