The long distance running wall - maybe I found it

Today I broke all my old records and managed to run 8.75 miles under 9 minutes per mile. I just decided to see where my limits are. That is where it is! I felt like stopping several times on the hills near the end. I stopped twice this time to take a drink. I need now to work on breaking through this wall. I have added a speed workout and strength workout to my weekly schedule to improve on this. Monday is my distance day, and I try to run at race pace to make it more beneficial.