running poor

I have a 2000 2.4 4 cilinder grand am with 200,000 miles on it. The problem is the car started runing slower and slower until it barly got in the driveway. The next day I purged the fuel thinking it may be vapor lock. Now the car will rev to 4,000 rpm and lacks power. If i try to rev higer the rpm drops back and looses power. I added fuel tretment it was the same. after a two days it was cooler outside and it ran fine. I tooke the car in for a new fuel filter. The car ran good for one mor day then back to rev limiting at 4.000 rpm. I din know if this is outside tempture is related but will not have a cool day again for a wile im in Las vegas.
Please help Iam trying to save this car for my son he about to get his licence.