A quick way to check for vacuum leaks is to get a can of carb cleaner and spray it around the base of the intake, throttle body and all the hoses. If there is a leak it will make the engine run different. Usually increased rpm's.

 

Have a tech with a scan tool check your CAM RETARD values. It's accessible from the OBD computer. If they're out of range (normal = +/-2 degrees), pull the distributor and check for a worn gear on the distributor. Another possiblity is timing chain slack or skipping causing erratic timing at the distributor.