We were on a road trip (1300 mile) across desolate WY, and my 2002 VW Jetta wagon TDI (120,000 miles) suddenly started losing power. I could maintain 45-50 mph up hills, but no faster, and this car usually has no trouble. We pulled into a remote auto repair, and had the mechanic replace my fuel filter (I carry a spare...). The car ran fine for the next 120 miles, then loss of power came back in the same way. Pulled in to a bit less desolate place, took a mechanic for a ride, and it acted fine, no symptoms. He blew out the air filter, I topped up the oil. There have been no warning lights, water temp guage is fine during both incidents. We need to drive back the 1300 miles next weekend, and are a bit nervous. What else could it be?