You da man Ken, thanks for the details.
Here is a rather optimistic graph for an electric motor for the readers (expensive large motor maybe?), I assume a generator is similar:
But both the generator and motor have islands of peak efficiency, like an ICE BSFC graph, except in a series configuration the individual inefficiencies are multiplied by each other. Mating the generator island to a bsfc tuned internal combustion engine is doable with an energy storage scheme, but the motor end still will be sub-optimal for most of the operating range, and battery losses when vehicle demands are not just right.
And of course constant cruise operation just screams for the additional expense of a clutch and sprocket hanging off the engine.
Ever looked at hydraulic energy storage?