Symptom sounds like fuel starvation.
1) Possible fuel tank lines restricted at the bottom of the tank, there may be a fitting that is clogged up depending on how its all plumbed in there. Had similar problem last summer with diesel John Deere units, every one had sediment strainer on the pick up tube full of dirt , years worth, blew it out with air.
2) Possible rubber fuel hoses getting old and restricted on the inside, replace all supply hoses.
Hope this helps.