Well, we're in a similar boat (I mean car), down to the 1.9% rate.
We're taking the middle road of paying it down pretty aggressively, but not at the sake of trying to invest as much as possible.
Arguments for paying down the car ASAP I suppose would be:
1) yes it's just 1.9% but it's a guaranteed return. This is an election year so who knows how the market will react if Trump wins,
2) you have to keep collision, comprehensive, etc. coverages on your vehicle as long as the finance company has the title (you would probably keep the coverages for a few years anyway),
3) paying down the car, which most people here would likely view as an extravagant purchase, depending on your exact situation, guarantees that you increase your net worth, whereas you might blow the money on entertainment, etc., with any money you "save" from not making the biggest payments possible (you don't sound like that sort of person though)
I know these aren't the strongest arguments, but you wanted to stick just to math!