World Champion Sebastian Vettel became the first F1 driver to sample the new Port Imperial circuit this week, which will host the Grand Prix of America next June. Vettel stopped off after Montreal in New York both to drive the street circuit, which is still under construction and to make an appearance on the popular David Letterman show. Vettel drove the track in a road car as part of a promotion for Red Bull partner Infiniti and described the circuit as like a street circuit version of Spa Francorchamps, due to the elevation changes. “It’s a pretty steep uphill and More…