Okay. Actually I misread your post the first time! Forget what I said.
So it cranks always, and cranks strong. It always Cranks though - not almost always, but always. Just making sure.
If that's the case it could be a fuel pump getting lazy and not building up pressure fast enough. Which could also mean the pressure drops when you turn the car off. Check the pressure before you start, and after you shut it off, monitor the pressure for a minute, then check it again after an hour. Unfortunatly for 2004+ you need a scan tool with the fuel pressure PID
to check the pressure. You can use the application toque and a Bluetooth OBD-II adaptor, all under $20 if you or a friend has an android phone or tablet with Bluetooth.
When you cycle the key on (not to start but just to on, do this 5 times in a row), do you hear the fuel pump "prime"? You may need to have a helper listen with the gas cap off if you can't hear it inside the car. It should do it EVERY time you turn the key. If it doesn't it means its time for a new fuel pump!
With the motor running fuel pressure should be around 40psi, no less than 30. If the pressure drops to 0 quickly after turning off we need to figure out why. If the pressure doesn't get up above 40psi for More than 1 cycle of the key to on, it could mean you need a new fuel pump as well.