Pontiac Grand am GT won't rev past 4,000 rpm, no rpm governer?

I have a 2001 Pontaic Grand Am GT. Just recently (a couple of days ago) it woudn't start. Then engine was turning over, but wasn't getting gas. My dad and I just replaced the fuel filter tonight, and now in park and neutral, the motor will NOT rev past 4,000 rpms. I put the pedal to the floor, and the rpms rev up to 4000, drop suddenly to about 3800 and then go back up to 4000 and do this over and over again. This is not a governer on my rpms. Before I had the fuel problem, it revved up to the max. I haven't tried to take it past 6000 obviously. When I am in drive, however, the rpms go past 4000. I only took it up to 4500 because I didn't have time or space to go faster. But it did pass the 4000 mark. What is causing this RPM restriction? It did not do this until the fuel filter started causing problems. any help is appreciated thanks so much