I decided to take my truck up on a highway drive to pick up supplies. It idles perfectly and run's great at speeds <45 mph. Once I get it up to 60 or 65 for a period it begins to lug. I can feel it jerking and lugging like it is starved for fuel. When on a hill I hit the gas and it just really sputters with no change in speed. I changed the fuel filter and adjusted the carburetor and it still does the same but not nearly as bad. If I just cruise at 45-50 it is not a problem, it's only at higher speeds. I was thinking of replacing the fuel pump. Any ideas guys?

 

Bogging down, hesitating, stumbling from a dead stop and/or when accelerating at speed: Defective accelerator pump and check valve. Both come in the carb kit or can be purchased individually.