4000rpm in the lower gears means your foot is like, 2/3rds of the way to the floor. There is no way 6th gear is turning 4000rpm@100mph, because even my tightly-geared 2.5iA with 5-speed automatic turns about 3800rpm @ 100mph. 6th gear should be an overdrive with super-tall gearing for fuel economy.

Let it break in a few thousand more miles.