Have I done the Impossible?

Have I found a way to pretty much kill all the Bermuda in my back yard? I started my lawn from seed two summers ago. The front is Yukon and the back is BlackJack. I live in Lenoir NC which is zone 7B. The grass in the back has almost completely died. There are a few sprigs here and there. The front is coming in pretty good. Last summer the back looked pretty good for a new lawn started from seed. I am thinking that I might have suffered from winterkill. The temperatures in April and May have fluctuated from the high 80's to freezing. I scalped the back in early April. Applied pre emergent in early April. Applied some fertilized less then 1lb per thousand. The ph in the back is low around 6 the front is 6.5. I have added lime this past weekend. I guess my questions are. Am I going to have to start fresh? Is the grass just stunted and slow to comback? Was it the cold or low PH? Is the Yukon just that much better? I am really frustrated and a bit discouraged by this. I was really looking forward to the third year as I have read that is the year the grass really takes off. Any suggestions would be greatly appreciated. Hopefully I made some sense I had to get this out quickly since I am at work. I have added some pictures of the front, back and the back from last year