OK, good to know. most American muscle 4th is 1:1 like the Tremec's - my TR6060 4th is 1:1 5th is a mild OD still pulls hard, when I did the Tranzilla build I shortened 5th so almost no RPM drop between 4th & 5th. The T56 is also 1:1 in 4th - these are the two most popular OEM transmissions on American Muscle. Are most JDM M6's 1:1 on 5th - that's interesting and I will have to think on that - maybe due to higher revving motor or rear end gear is 2 and change - again interesting and thank you for information.Wrong assumption- for a six-speed gearbox, fifth is usually 1:1 and sixth remains an overdrive. Nissan won't want to spend millions on recertifying the drivetrain alone.