You may be tired immediately at warmups because your nervous/anxious to compete, so u might subconciously feel that u need to save energy, but instead u should get blood flowing, i (personally) always run 2 laps then do jumping jacks then stretch, then push ups if needed and try to get my blood flowing so that my energy stays high.
As for conditioning urself, i firmly believe that all the conditioning won't help as much because, everything u do, u will wanna do better and therefore take more energy.
Example: Ur used to throwing ur routine, but as ur endurance and strength goes up, u put the effort to making all ur passes higher and tighter, and making the stunts hit harder and stay more sturdy, thus ur % of energy at the runnign tumbling is somewhat similar.
Solution for me and other ppl on my team: When im at practice, I ALWAYS throw tumbling and jumps, even when they ask for just a stunt run or coreo run, if i feel like ima die, i still do it. gets my body to do it easily, not only that, but most importantly, if its at practice, and u do several full runs, it will not only "condition" you, but u will learn the pacing of ur routine so u know when to breathe, and whens the best time to take it easy, to save energy.
That may of been long, but i hope it helps