Recently my car has been trouble starting up. It will usually start when cold, but not as quick as it should, seems like its not getting enough juice. Last week I replaced the air filter, plugs and wires, and put in a new battery. After the car has been running it will not start back up, again feels like it is struggling for power. But i have lights and radio. I took of my alternator and had it tested twice, both times was good. Now it has begun stalling, generally while in drive, at a red stoplight or similiar situation. If I shift into nuetral it will idle a little higher and usually will not stall. When trying to start after the engine has been running, it seems it will start if i keep turning the key and giving it gas at the same time. In order to keep it from dying I must keep reving the engine up. Maybe something with not getting enough fuel? Any help would be great, thanks guys.