A tidbit of info on the 368 engine. Often overlooked because it's so darned hard to see.The EFE valve which is on the exhaust manifold, passenger side.The purpose is to direct hot exhaust gases through the intake manifold during cold startup. The shaft on this valve must be kept lubricated and moving freely because it is operated on vacuum only.Some of the symptoms of a sticky or non functioning EFE are as follows. Poor operation at start-up(rough idle, stumble) Poor operation after warm-up (lack of high speed performance,surge,miss at all speeds) The EFE is controlled by the TVS (Thermostatic Vacuum Switch) on the 6.0 and electronically on the 4.1 engine. The TVS is located on the left front of the cylinder block . Make sure the vac. lines to the EFE are sound and have tight connections.