I have a 94 NPR gas that has been reliable for years. We had just finished up a job and had a trailer hooked up and were checking the lights. It was idling fine then started surging for a few seconds and died. It started fine, but was down on power and would not idle well. I needed to get the trailer to another site, so I just pushed on. After a few minutes, power was back and it ran smooth again. It started acting up again before we reached out destination. Since that time I have parked it and now need to find the problem as I need it operational again. I thought first I should change the fuel filter but I can't find it. Any of you had similar issues and can steer me in the right direction?