We have a customer's Toyota 42-6FGU25, frame # 68662 equipped with a 4Y and a duel fuel ("convertible" in Toyota speak) that gives us diagnosis problems. It has approximately 8000 engine hours. When the operator drives across the yard at full speed, pedal to the metal so to speak, the truck will run fine for a short period of time then start to sputter and lose power and sometimes completely stall. If you shut down the machine for a few minutes it will start right up as if nothing was wrong. We know that the machine does this when the operating temperature is normal but we as yet do not know if it does it when the engine is "cold". We have done the obvious stuff, tune up with plugs wires cap and rotor. As well we installed a new regulator. We also have spent a lot of time on "adjustments" particularly on the dual fuel carb. Has anyone else experienced such a situation? I'm looking for advice on what the next thing we should look at. I have also posted the same question in the Mechanical discussion forum.