Hesitation after engine warms up.

Possiblities are;
The fuel pressure regulator
Check the fuel pressure itself
Check Throttle position Sensor
Check MAf/MAP sensor
Check intake tract for restrictions
check for vacuum leaks
Check exhasut for restriction, especially at the catalytic onverter.
The camshaft and crankshaft position sensros
Incorrect isntallation of timing belt as this would throw timing off, so check timing as well.

You can run trouble codes at most Adnace or Auto Zone parts stores for free.

Let me know what the outcome of the above is and we will go from their.