Just lower your positional sub in sub out rating requirement. As stated I use 85 in, 80 out. But depending on how you run your team. You may want to try 75 in, 70 out. The schemes you play with may be too aggressive to be sustained the whole game.
Just adjust the positional slider subs to fit your schemes. Teams like Cowboys, Seahawks or Patriots don't sub players the same way. They all sub players based on how and when they want to use them for certain situations. You probably need to learn to chew up clock with an above average run game or short passing game to keep your offense fresh.
Also you may want to improve on getting better at getting 3-and-outs on defense. I don't know what to tell you. I designed to sliders to be simulation so there weren't any Roadrunner players with boundless energy. Another reason I like the settings is it actually makes that stamina rating mean something.
Superstar players aren't only defined by their obvious athletic ability. They should have the stamina to be consistent all game. Players like Jerry Rice and Deion Sanders and J.J. Watt are prime examples. I only play 7 min quarters. If you play longer than that, try dropping the fatigue slider lower to account for quarter length.