I had a little different problem, i replaced a rotted rubber section of my fuel tank vent line. Every time after that, when i mashed the Go peddle it would run out of gas before i got thru 1 gear. Ended up that the metal part of the vent line was full of bug, and when i took the rubber line back off and blew all the trash out, problem when a way.
Have you done anything to it lately that many point you to the problem.