Cranking but won't start in extreme cold

I have been having problems getting my car to start when the temperature is below 15 or so degrees. And since it's been below zero for the highs here in Minnesota, no chance in starting it. It has started when it's sunny and above 20 or so, but it still cranks for about 7 seconds before starting. Sometimes, I have to spray a bunch of starter fluid in the intake to get it going. I also poured one bottle of isoheet in the fuel tank, and there's a full tank of gas. The battery was replaced about one week ago, and I confirmed at Autozone that it's putting out good power. The ignition coil was replaced one month ago, and the spark plugs were replaced two years ago. I heard that the MAF sensor could be causing issues, so I cleaned it with MAF sensor cleaner. I have heard that I should probably test the sensor. Does anyone know how to do this? Also, any other thoughts as to what could be the issue?