I'm not a tech. But it seems like that dead spot should be turbo boost. On my 2000 F350 Auto, cruisin along and then getting on it on a hell it rattles and ALMOST bogs (sounds like you just hear the engine go faster and louder), then the tach just shoots from 2000 to 3100 in less than a second and that boost gauge is climbin. Maybe you have a jacked turbo or a massive boost leak, I have no idea for sure, but it's an educated guess at least.