Mercedes Benz repair: 1976 300D stalls at high speed, catalytic convertor, fan clutch

Question
The car only has 300K miles on it, and would gradually loose power and stalling after being driven 2 miles, so I changed the fuel filter.  Now it gradually looses power and stalls after 15 miles.  Restarts OK after waiting a minute.  My mechanic says the fuel is not bad.  The car idles fine, never stalls at idle.

Answer
Is the car have a catalytic convertor, Im not positive on the model but if it does it sounds like you may have a clogged cat which would leave you with loss of power when driven try driving up a hill and punch it and see what happens if it has no cat, when was the last time the tuneup was done plugs wires etc? I would start there. I do not know where you live or if there is an aftermarket exhaust in your car ,anyways do a compression test on your cylindes and see if you have cylinder compression in each cylinder that is within 10 percent of eacch other if not your motor is shot, then i would suspect your fuel pump so  juump your FPR 87 and 30 and check it . I would suspect though a compression problem. what is your thermostat guage reading nominal temp is 80-100 celcius which if it is running hot will stall out the engine then i would think a fan clutch