Greetings fellow enthusiasts. I have a frustrating intermittent problem with my Ford Ranger V6 petrol. When I accelerate she does it beautifully up to about 3500rpm. Normally the revs rise in typical V6 fashion but on occasion she suddenly starts losing power and the revs drop gradually. Sometimes it kicks in again at about 2000 rpm and she accelerates like the blazes, and other times just sticks there. This sometimes happens when she is under load e.g. travelling up a hill or overtaking. The frustrating thing is that this is intermittent and as always it doesn’t happen when you take her to the workshop and plugged into a diagnostic computer. We have tried a number of things e.g. new fuel pump, spark plugs, plug leads, etc. No joy. It feels like a fuel supply problem as if something is blocking the fuel supply once the flow reaches a certain minimum. When the flow drops the obstruction retracts and the flow is restored. A possible clue to our mystery is that I have managed to burn a hole in my reasonably new free-flow exhaust. Does this mean that the fuel mixture is wrong? Maybe the fundis can tell us if a throttle valve might be sticking that is supposed to be opening up at 3500rpm? Another suggestion I have heard is that the Ford has a duel fuel line from the tank and that at high rpm the second fuel line comes into play. A damaged second fuel line within the tank and the subsequent loss in pressure would explain the mystery. This does not however explain the intermittent occurrence. I keep coming back to an electronic problem. Your thoughts are appreciated.