Anyone explain why this two sets of prints are so radically different

These prints were made right after one another with the exact same settings. Was printing beautifully for about 45 prints and then this started and it has not stopped. The before prints were being printed at an overall reduced print speed 30mm/s across the board and a lower temperature 200c. Worked great until it didn't. Any thoughts any one? Can't get it to print anything nicely now. MakerBot 2 Firmware 7.6 About 1000 hours total build time. I have purchased a new extruder assembly to see if that helps.