Well, as soon as my last match was over my instructor came up to me and said "You see why we spar for ten minute rounds!" I don't remember gassing until the last round. Do interval training, all kinds. But there is one other important thing too, I'll mention later. Interval training is like doing a bunch of pushups, situps, squats, burpees (the best) in 3 minutes, and then rest 1 minute, and repeat. There is no way you can fully recover in one minute, so the next round you do you have to force yourself to go 90-100% with only half your tank full. If you find the right combination of exercises, you'll see a big improvement in recovery time between rounds and bigger numbers in the interval rounds. You can do running too: Run 200/400 meters, rest x amount of time. There's lots of stuff on it online, but I recommend
www.rosstraining.com and buy one of his books, best thing ever.
The other thing I mentioned was learn how to use your energy while fighting. Don't tense up 100% of the time or you'll burn out. When I'm on top, I don't waste energy by clamping the guy everywhere, I just put pressure where I need to so he can't escape. And I only used one sweep the whole tournament. I can do that sweep very easily and I recommend that if you don't want to waste energy, have a couple sweeps/attacks that you know really really well so you don't waste energy fighting the whole time. As soon as I was in half guard, I hit the sweep every time. Only the first guy gave me trouble.
A guy I just lost to told me that he had been doing tabata intervals and his conditioning went through the roof. See if it helps.
I went to another tournament after that, got the silver. It was a gi tournament and the guy I lost to was a 3 year white belt who got passed the first round of the adcc trials. He put a clinic on me. There were 5 fights again. I thought since I got gold that I'd be a little big shot, and I neglected my cardio. He killed me. I think our weight has the most amount of people in it. So prepare for lots of fights. I kind of wish it wasn't that hard, but it just makes the win more rewarding. If you're within your weight, make sure you eat good food before the fight!! I was dizzy and not feeling well because I thought I needed to lose a little bit more so I barely ate anything the day before. Eat a little sugar before every match to wake you up since you have to wait awhile in between matches.
Try not to be nervous. My first tournament, I was peeing every 10 minutes. It was ridiculous haha. I've been training for 9 months now, in case anyone is wondering. I learned the triangle escape that saved my last fight the day before the tournament haha. I was thinking, this is really good, I should drill this a lot.