2002 Pontiac Grand Am hesation

Hello was wondering what would cause a hesitation at certain speeds, it almost like its not getting enough power to speed up. I have replaced sensors related to this problem and the problem is still there. There is no check engine light on, I also bought a new o2 sensor. I also checked for vacuum leaks and there was no leaks. What happens when this does this is the rpms move up and down when accelerating(for instance when I slow down and the speed up again) while driving. I have read somewhere that it could the egr valve which is electronic egr valve that I have. Could these be cleaned out and how. What is the difference between a electronic egr and manual valve. Thanks