So, my Pathfinder had been running okay but having some lagging acceleration on hills etc. Then the other morning it didn't want to turn over, started then died~all interior lights etc. all working. Started it again and it drove fine for about five miles and then started stuttering and died on the side of the road. Towed it home and now it will turn over after a few tries but dies after a lot of stuttering. Did a spark test as recommended in other posts and i'm getting spark. Replaced the fuel filter, didn't make a difference. What else? How do I test the fuel pump? Could it be a timing belt issue?