The original behavior you described of revving when getting on the highway is completely normal on this vehicle (either that or mines screwed too but seems to work fine). The manual describes that the engine will rev higher than "normal" vehicles...

The long and the short of it? I don't think theres a thing wrong with your tach. or your FEH. It sounds like this dealership IS NOT interested in keeping the customer happy, I'd find a new dealer. There are plenty that are.

It almost seems as if at best case they don't know anything about hybrids and are covering their butts because they should have known there wasn't a problem with the high rev in the first place or at worst case someone at the dealership is trying to pad their warranty work for extra cash from Ford.