I have had a similar problem with my 3340, power loss on my tractor comes from loss of fuel, thought I had a air leak from the tank to the pump, (kept seeing the factory sediment bowl half full of air and fuel) replace the lines, thought my pump was failing, removed the pusher rod and reinstalled the pump, and replaced the pumping unit with an electric unit, mounted a sediment bowl and new electric pump at the front of the tractor near the air cleaner, ran all steel lines except for couplings, still getting a air bubble in the sediment bowl after tractor has been shut down for 10 min. but do not have any loss of fuel when running, assuming the sediment bowl is defective and when tractor is shut down, the fuel supply line wants to back drain into tank creating a vacuum on the sediment bowl and sucking air in, I am eliminating the sediment bowl and replacing with large canistor style inline fuel filter.
Have been plagued with this problem for several years, it comes and goes, ususlly comes when I need the tractor the most.
Hope some of this information is helpful.
Eric