95 ford f250 diesel 78,000 miles. Starts, idles and runs fine up to about 35mph. At 60mph it starts bucking- a little at first- then almost stops the truck. Pull off the freeway, wait 10 minutes and it starts up and runs for a few minutes without cutting out. It takes a long time to get home at that rate. Is it poor fuel, (new filter 6 months ago) algei growing in the tank? air getting into the fuel system. The tank is full and has been but the truck did sit for about 3 months without starting (I was away). The oil if full. Where should I start looking? Thanks Art

Thoughts:

On diesel engines that will not restart, after they are warmed up, it's often a sign of a tired fuel pump. As they heat soak, inside pump head clearances increase and it will no longer develop sufficient fuel pressure at cranking speed. While it's running, fuel helps cool the pump by carrying the heat away.

Be sure you also replace the under frame fuel filter. If you decide to replace the fuel pump go Motorcraft.