Went to track, weird timeslip!?

[Blaster]

I took my 91 GT out to the track last night for the first time with it's new N/A 331 and ran a 12.87@106, 13.00@106, 13.00@106, and finally a 12.85@106. Adjusted altitude was almost 3500ft last night. My 12.87 run was a 1.91 60ft but my 12.85 run was a 1.82 60ft, what gives??? I did hot lap the car when I ran the 12.85 but could the engines heat kill the power that much???? I would have though gaining a tenth out of the hole should be worth way more than that in the 1/4, even if I did back to back runs. What gives, is running hot (my temp gauge was just over the 1/2 mark) that bad??? Could it be my new 27" ET street's are killing power somewhere??? Or do i need more than 3.55's???