95 PSD hard starting question

I have a 95 Powerstroke f250 and in the last couple days its not wanted to restart when its been running (for example at the gas station) It turns over like a champ but wont ignite. If I let it sit for 30 min. or so it'll start, but even then the motor has to turn more rotations than normal to catch. I tried to drain water from the filter but none came out. I'm going to walk to the parts store and get a new fuel filter in case that's the issue, but it doesnt seem like a restricted filter would be a sporatic nuisance. It only happens when its been driving for a while. Any leads would be very much appreciated. thanks, chris