Hesitates and stutters after warmed up. When first driving I can press the accelerator as hard as I want and the car will respond well - no hesitation or vibration/shaking. After a couple of minutes (warmed up) when I press the accelerator the car will stutter and vibrate. I have to press the accelerator very slightly to increase speed. This is a problem when trying to merge into traffic and happens at any speed. The tach seems to show rev's OK. I can put it into neutral and hit the accelerator and it will not stutter or vibrate. I have already replaced the MAF sensor, SeaFoamed the throttle body, took the EGR valve and manifold off. I cleaned the EGR manifold and tested the diaphragm - it will move under vacuum.