I to have had the hesitation problem.
I found it to be the "over sensitive" knock sensor.
This was al over the board about a year ago.
After i modded my knock sensor, the problem is gone, it only comes back when i get a bad tank of gas.Even then it rairly happens.
The theroy is, the sensor is to sensitive and picks up things that the ECU thinks are knocks/pings and decides to retard the timing.
1-2 rubber washer made from a bike tire patch, worked for me. The rubber is about 1/16" thick or less so when you tighten down the sensor it skwishes and is almost NOT there. It dampens the knock sensor kinda like dynamat.
(insert non-responisibiliy discloser here)
Seem to work great for me....