Trying to assess what type of grass this is growing in my Dallas, TX (8a) lawn and would really appreciate someones expert advice on some of the issues. It was planted via Sod and the the first photo below was taken April 11th 2017. It seemed to grow into a decent lawn by May 24th 2017 (2nd photo) Once early August came around the grass has slowly begun looking sparse and less dense. Especially in shady area underneath crepe myrtles. Any advice for:

What kind of grass is this?

What would you do as of 9/26/17 to get it back into shape? (winter rye, etc.)

How would you deal with grass no longer really growing much under shade/slope?