saturn sl1 trouble

i have a saturn sl1…until recently it ran great, but now it hesitates like it doesnt want to accelerate…to the point it wont go over 45 mph..also the rpms shoot up to 4 before it wants to accelerate at all…it wont accelerate at all on any type of incline either…it also revs sounding like a bad muffler job lol…when i first start the car and go it is fine until i come to a stop or the engine warms up..if u could give me any insight it would be great …thanks