I have noticed the RPM drop issue too. If I am correct this is due to the fact that the tiptronic locks the torque converter and that is the RPM drop you feel because when the torque converter locks there is no longer slippage between the engine and transmission. This is what seperates the tiptronic from other automatics with manual shif mode. You will notice this if you drive in manual shift mode. once the torque converter locks the engine is lovked into the transmission and drive train, and it will feel like a manual transmission when when you let off of the gas and get back on it. Thats is one of the nice things about the tiptronic is that it locks the torque converter in the lower gears as well to get all of the engines power to the wheels