Hey,
Cramping during long rides can be a real bummer, but there are a few potential causes and solutions you might consider. Even though you mentioned hydration and electrolytes, it's still possible that your body needed more of those elements. Gatorade is a good start, but it might not be enough for a century ride. You could try using electrolyte tablets or supplements, which often contain higher concentrations of essential salts.
Another possible cause of cramping is muscle fatigue. When you're climbing hills or maintaining a fast pace, your muscles work harder and tire more quickly. To prevent this, you could incorporate more hill training into your routine to build up your endurance. Additionally, consider varying your pace throughout the ride to give your muscles a break.
Lastly, it's important to ensure that you're fueling your body properly before, during, and after the ride. Make sure you're eating enough carbohydrates and protein to sustain your energy levels and aid in muscle recovery.
Hope this helps, and happy riding!