What is your setup?

I spoke to my good friend who is a tuner, its likely it is the above scenario that is happening.

 

I have a vortech sc with base 7 lb pulley. Stock ecu and injectors and the 255 walbro fuel pump.
I run lean WOT like crazy too. Some how fixed itself a couple months ago but then a pulley broke off and when everything was put back together it's back to being lean lol.
Seems like the hesitation only happens sometimes. Today it didn't happen at all. Somehow it seems like when the car is hotter and it's hotter outside it runs better.