OP do you have any other mods that you haven't listed? Gaining that MPH in the back half is a big deal. Not saying it can't be done, but usually its done with more mods. That being said conditions were very conducive to good times...
Things that would help you here.
-Posting some datalogs of your car if you can. This would give us a good idea of how much power your car is making.
-A video if you have one, of the run.
-Slips of other runs that were close.