If you aren't already doing so, try eating more meat. Especially for dinner the day before a big ride -- longer or harder than usual.
I've tried many diets but nothing else I've tried is a satisfactory substitute for meat. I get that same "empty" tank sensation when I tried a primarily vegan diet in 2018. Besides feeling empty all the time, I can't digest legumes even with the help of digestive enzymes. Gave it an honest try but my body and a vegan or even vegetarian diet don't get along well.
Even cutting back and substituting chicken or fish didn't work for me. I like pork too but usually eat beef at least three meals a week, often more. Especially the day before a big ride. I'm planning on putting in some miles this weekend, so tonight I'm eating steak, and for breakfast beef liver and eggs. At the very worst I'll pedal easy the first hour to ensure good digestion, but I have no digestive problems with meat. I even like fatty brisket (as long as it's hot), which grosses out some folks.