My 07FJC 4WD 58k miles has developed a strange and very annoying surge when the engine is lugged between 2000 and 3000 RPM. When you are accelerating very slowly or at full speed, the engine runs fine. However, when you are accelerating moderately, but not enough to cause a downshift the engine will hesitate two or three times when going through this part of the power band. I have brought it to the dealer twice and they have tried cleaning the fuel injection and syncing the throttle bodies to no avail. They say there are no engine codes. I can't tolerate this anymore. Any suggestions?