A couple weeks ago I started experiencing slow start up, car turned over then stuttered and I had to give it gas for the engine to stay on. Don't know what it is as I have a new alternator, battery so I'm thinking maybe it needs a tune up or maybe it's the fuel filter needs to be cleaned.

What other symptoms can it be and how difficult is it to fix? The fuel pump filter might be the problem.

 

I had a similar issue a while ago. It had a rough idle but the engine would stay on if I constantly pressed the accelerator. Eventually it was bad enough that it would even stall when I changed gears. I was trying to park, changed into reverse, and it stalled. Does this sound like your issue? Is your 'Service Engine Soon' light on?

Also, I might be wrong about this, but I think the fuel filters are non-serviceable (or at least Nissan claimed they didn't need changing).

 

Probably cranking speed. ie. bad connections or bad starter.

If you ahve a OBDII scantool plug it in and monitor your cranking RPM (before car starts up/catches). If it's under 250 there's a problem.

It could be due to an idle issue, intake leak, etc, etc, etc, but the car should still start up.