I like the idea of forcing the ABS to kick in in case there's air in there. Some GM's will have a soft pedal until you do this. Standard bleeding procedure is to start with the caliper furthest from the master and work your way to the closest one. According to the bleeding sticky, you need the key on and pedal partially depressed for the rear brakes as the electric motor pushes the fluid out. Obviously keep the level topped off. When I replaced my lines, I followed those directions but still had a soft pedal. I found my front calipers were toast. Replaced those and followed the procedure again with no issues. Point is, don't assume the calipers are still good. Some folks seem to be changing them on a 3 or 4 year rotation, especially in the climate we live in.