One problem related to transmission shudder has been reported for the 2004 Infiniti G35. The most recently reported issues are listed below.
Heavy vibrations from the transmission/motor when stopped and in neutral w/o the air on. Feels as if the vehicle wants to stall when it vibrates. Vibrations get worse when driven at high rpm's. Infiniti dealer tech advises that it's a transmission problem but Infinitis corporate office claims its normal.