It might be the ECM or the connections between the throttle kicker's switch and messaging to the ECM, check to see if the kicker isn't the problem, but i doubt it, but if it is, the ecu isn't getting the message from the kicker that it needs replacing, because it's a minor defect of the kicker. To check the kicker you need to pop the hood and check your throttle lines and the kicker looks like a baby hand sized torque converter. when ever the gas pedal is stepped on the kicker is tugged when the throttle is stretching when opening. It might not be tugging the kicker right away and not giving you that automatic kick, but istead pulling the throttle fa have a sec and then pulling the kicker which gets you to thinking it is hesitating.