The diet sodas probably are less hydrating than you think, due to the slight diuresis induced by the caffeine. You do get some salts out of em though. In addition to just drinking more water in general, I'd either cut the gatorade 50/50 with water, or probably even a better idea would be to swap it for coconut water completely.
Adding some powdered BCAA's to your water in between meals may help you get more fluid in and as much as you are training, fluid an electrolyte status is not something to be messed with. Also, you're salting your foods, right?