Here are a few suggestions.
The map could be modified to allow for more sea movement. You could add the St. Lawrence Seaway, a network of canals and locks that opens up the entire Great Lakes to moderately sized ocean going vessels. And you could add the Panama Canal, which would make John very happy!
ToTPP allows an additional flag that allows ships to move along rivers. Perhaps create a riverine unit with this flag. It can only be used by a human player though - the AI doesn't recognize it.
Add units with AA capability. Maybe a strong one with zero movement and a less powerful mobile AA unit.
A spy unit in a city can block diplomats trying to steal technologies or sabotage. I'm not sure about blocking a bribe attempt, but it might be worth checking.
I suggest changing the name of the "Indian" civilization. It's no longer considered correct or respectful. In Canada, we use the term "First Nations" or indigenous. I don't know what they use in the states, other than Native Americans.