Is my boxster broken??

[myn8m3is8ndy]

I have a 2002 tiptronic Boxster. When I'm driving down a hill, my speed slowly decreases but rpms goes up. Im not stepping on the brake or gas pedal. Just letting the car glide but the rpms....omg bothers me. When I drive a bmw, toyota, honda etc, (all automatic, same circumstances, same hill, same everything) the car just rolls, gets faster due to gravity and momentum and the rpm stays around a constant 1k. Also i noticed that this happens on the freeway too. When I'm going straight on a declined road, my car slows down...like what the....shouldnt it gain speed instead of losing speed?? Is something wrong with my tiptronic boxster?? or is that normal??