Was original lawn fine fescue? Not good in heat. Was there a high percentage of perennial rye...not good above 90.
However, when you reseed you are forced to use a percentage of perennial rye, as it has good seedling vigor. Kentucky bluegrass will seldom give a good "take" it just comes in too slow. In any event use top-quality seed.
If you want Kentucky bluegrass--use sod. Let the experts grow it for you.