1976 607D Cuts out while driving

I have been helping my friend who owns a 1976 607D Mercedes Camper van.The van is used at 6000 feet elevation It appears to have a 240D motor.It has 120,000 miles on it The problem is that once you start driving it it while run fine then it will cut out and loose power as if it is starving for fuel. It does this sporadically and once it cuts out if you let up on the gas pedal it sometimes will kick back into power and sometimes it will just die and you have to pull over Then sometimes it will start up immediately and sometimes it needs to set for a few minutes. It has all the fuel lines replaced new fuel filters and clamps. All fliuds have been checked including the pump oil level. It has a clear plastic filter that is placed ahead of the pump when it dies it appears to have 1/8 level of fuel in it. It also has a roof missing idle at times. Thanks for any help..

I just wanted to list this as a 207D not as the 607D!!