According to Edmunds.com, in 2005 one of the changes was that

"...the manual transmission has been improved to provide a lower shifting effort..."

http://www.edmunds.com/infiniti/g35/2005/review.html
(see "What's New for 2005" section)

Are there any 05-06 MT owners that previously owned 03-04 MT that can confirm this? I am just curious...I changed the MT fluid in my 03 to Amsoil and it's still hard to shift (compared to any other MT car I have owned or driven).

 

the manual tranny has undergone several revisions. i had my '04 tranny replaced under warranty in '08. the new tranny was a revised unit, requiring a new clutch disk. overall i don't notice much difference, but maybe slightly less notchy with the 1-2 shift. "shifting effort" feels unchanged, however.