The grip glue is made so the grip can be un-installed but at the same time to grab enough to keep the grip in place under pulling-pressure over the years and also to stick in high ambient temperatures.
I usually lift an edge of the grip and shove my thin air compressor nozzle between the grip and the bar, then wrap my fingers around the grip to seal the air in and give it a few shots. The air lifts the grip glue quickly and the grip can then be rotated off as usual. If needed, a little WD40 will help it slip off once the grip glue has been loosened, then just clean it off before re-installing. Hope this helps.