As you say your calves tighten up on the treadmill. I am guessing they do not tighten up on the basket ball court.
Your goal is to run circles around the guys you play b-ball with and lose weight.
To maintain muscle I STRONGLY suggest you use BCAAs then do slower lower intensity cardio in the AM before you eat.
Then have oatmeal and eggs after the workout.
As for running faster on the court and better endurance get on the court and play PLENTY of b-ball. If that means playing on another team then do it.
I wouldn't bother with the treadmill for getting better on the court but would use it as I said above at a lower speed but higher intensity meaning elevation but do NOT hang on to the handles when you do this.
Work your way up to 30 mins 3 - 4 times a week or even to 6 times if you feel the need.