My truck is starting hard. Usually takes multiple tries. It almost catches and fires up but won't until the third or fourth try.

It's not throwing any codes, so I assume that all of the glow plugs are working. The glow plug relay is a month old so it can't be bad, I hope. It's belching black/gray smoke so I assume its getting fuel. I already changed the fuel filter so it is new.

Could I possibly have some rotten fuel. I also added a healthy amount of anti-gel (maybe the stations switched to non-blended, it has been chilly) So I am trying to see if plugging it in helps. Could the other fuel filter be bad, the one underneath the truck?

I'm stumped.