MY '80 300SD was acting strangely when the fuel in the tank got below 1/4 full. I drained out the fuel (~ 20 gallons) by taking off the end of the rubber fuel line where it connects to the steel fuel line. That way it was easy to direct the flow into 5 gallon buckets. The fuel ran out fast until the tank started to get empty. When the flow was almost nil, I removed the in tank fuel filter which comes out from the bottom of the tank. This filter which is really a screen, was plugged about half of its height. So I cleaned and replaced the filter and put the fuel back in the tank. I haven't run the car low on fuel since, so I don't know if this fixed the problem, but the problem found matched the symptoms.

To make a long story short, what I suggest is that you check your in tank filter. It costs nothing and isn't a difficult job.

P E H