Filter sounds likely. Maybe crud in a fuel line?
I once had a piece of debris in a gas tank that was just floating around near the bottom. If I ran the engine flat out for any period of time, the increased suction would draw the debris against the outlet port, blocking it and causing the engine to stumble. It would recover once it was at lower revs and the suction was reduced enough to release the debris. Drove me crazy for months until my fuel gage sending unit started going and the fuel gage would go from 3/4 tank to empty in a heartbeat. Found the debris when I drained the tank and R&R'd the sending unit. Suspect the debris came from the sending unit. Bust out the flashlight and have a look in your tank - maybe a cheap & easy one to fix!