2005 Saturn Ion Cylinder 3 Misfire

I keep getting a cylinder 3 misfire on my vehicle, sending it in to a sort of "limp mode". It most frequently happens when I am low on fuel, but also happens when I go up long hills or grades. Sometimes it is just random. The code that it sets is p0303. No CEL comes on. I already changed the fuel filter and ran through some fuel cleaning stuff.