Problem with diesel in tractor?

I have a 1977 Ford 3600 diesel tractor that for the last 3 years around end of August tractor will die like it has run out of fuel (even though there is plenty of fuel in the tank). The first year this happened I had a new fuel filter installed. I was told it lost its prime. Every year when this happens I drain all fuel from the tank and dispose of it. I then take off fuel line from tank and blow air from compressor into tank to hopefully unclog what is blocking fuel from leaving tank. The first year I even took a shop vac to the inside of the tank to try to suck up any foreign objects that might be in the tank. I then refill completely with fresh diesel only to have the problem occur again the next year. I never even use that much fuel out of the tractor and in the winter I make sure to keep it full at all times. Any suggestions on how to correct this problem from happening every year would be appreciated.