I've been trying to imagine the 4th to 5th shift, and googling other transmissions. I think you did it right because you have a good lower first and second to get rolling or get out of somewhere, but the 5th for mpg. A little higher 4th might help a little i bet (??) but that seems a lot more difficult.
We just need to find a little more low end grunt from these engines. Delta cam's make a torque cam? Something with power from idle to say 4000?