Changing parts at random is the expensive way to not fix your car.
Step 1: using a scanner with live data, what are your fuel trims at idle, 2500, and 4000 RPM?
How consistent is the hesitation? Every time, occasionally? On full throttle, part throttle, both? Throughout the acceleration, or just for a moment? Is it worst at a particular RPM range? Any noticeable noises?