I have a 96 SL500 which intermittedly will hesistate going down the road. it can be after driving it for 5 minutes or not until 30 minutes. it has a mind of its own. the car will jerk [not backfire] like it is not getting any gas. would this be the fuel filter or fuel pump. how do I tell the difference? the car has 101,000 miles and I have had it for about 30,000 miles or 3 years and not have changed the filter or pump. I have no idea of what work was done before I bought it