Agree with Andrew here - NEVER EVER use anything else BUT Nissan OEM transmission fluid. Forget about what mechanics at other shops tell you.
When I first bought my V35 6mt, the gear change wasn't smooth, 1st to 2nd was a bit notchy. Dropped my car off at Nissan for gearbox oil change, specified to the mechanics it's a 6 SPEED MANUAL, the SAME one as the 350Z. After the oil change, it's been driving like a dream.