Hey so this problem is getting worse and worse. I have a 6mt 03 coupe. I can't shift into 5th gear. It was tough before but now I can't at all. Going into 6 is tough too but I can go from 6 down into 5th but can't go up to 5th from 4th. When I try to put the shift **** in 5th position it just ends up in 3rd. Don't know if anyone else has experienced this or knows what the problem could be. I was thinking maybe the bushings? Any tips would be appreciated. Thanks in advance.

 

Sounds like a linkage issue, not just a bushing.

 

Sounds like time for new transmission, unless you want to go thru the headache of pulling gears and putting them back together. 5th and 6th gear sounds like the retainer springs are gone! Pulling the gears apart is a headache is you dont have the right tools and more of hassle to put everything back together.
Not to sound like "debbie downer" but if 5 and 6th and messed up I can only image the heat spots on your flywheel and the disk is probably worn down past the rivots.

 

how many miles do you have on your car?

have you changed the transmission oil yet?

 

http://www.nicoclub.com/FSM/G35/Coupe/2004/
This website has the complete car manual repair, replace, and troubleshoot.
The section you are after it the "MT" section. In this section it will show you how to pull your tranny, pull apart gears and the tools needed.

Right now, 2004 6spd has aprox. 87000 but when I bought it from "CarMax" with 85000 still factory warranty (vOIDED). I'm running custom longtube headers, custom single catback, tb spacer and, aftermarket fuel injectors, m45 suspension, stage2 6puck CC and oem resurfaced dual mass. With just that small amount of mods I change and clean out bell housing ( shaving dust can do more damage than you think)MT fluid at around 5000-10000 depending on how hard I am running her. Oil change and spark plug every 500-1000 miles. I do this because it is not tuned and I have not flashed ECU so the automatically I'm hella off on fuel to ratio and burning the **** out oil.

The misconception a lot of people seem to forget about g35/350z is that they are not designed sport cars they are luxury sport. That 29lb dual mass flywheel is not designed for high shifts passed 3000rpms. One of the main reason everyone first upgrade should be drivetrain.