No loss of power of player on other team 6 mins on ice

Hi there. At :22 you can see his energy was almost full. At :52 he's under half. They are spending energy in this case. Also, they aren't being hit and they don't look like they're hustling. So, they're most likely gliding off-screen and getting energy back. I'm not seeing any issues here.

There are a couple of times you're double teaming the carrier. This means you're pulling one of your players out of position and expending additional energy. That's going to cause more energy loss. Try to make sure you're switching to the player that can best make a play. You're frequently letting the AI play D while you chase the carrier. This leaves more open ice for your opponent to find good passing/shooting lanes. Switch to the player that can best defend the play rather than committing 2 players to covering the carrier.

 It's also good to cover the puck. I get that you want to keep the action going, but this comes at the expense of tired players. Which means their ability scores drop. Let your goalie freeze it so you can get fresh legs on the ice.