I ran a hilly 10 mile this evening. It was a hard effort for me. I ran 64:27. A few months ago, in similar shape, I ran the same course at the same effort in 60 minutes. Temperature this evening was 80-85 degrees whereas last spring was in the 60's. The question how much time can I take off for temperatures 20 degrees warmer?
It's all in your head, don't worry about the temperature. You're just in woop ass shape compared to your previous effort, nice PR.
About 4:26. Looks like you're regressing.
It also depends on the humidity; you can probably find some tables with the info. But moving from comfortable temps to very warm temps, you probably need to add at least 10 seconds/mile. Also don't forget that if you are in a higher workload, you might just be more tired.