I had trouble with the Grade 5 bolts as well. I ended up stripping several of them. Very tight fit. However, I found that if I torque the nut good and tight and then hit the end of the carriage bolt with a 2-pound sledge, the bushing would move a couple of millimeters. It was slow, but it worked. I used several heavy duty washers on the end of the bushing so I didn't damage the bushing when I hit it. I used this method to remove the old bushings and to install new ones.
