I don’t know what “everything” you’ve tried is, but if I were at your computer, here’s what I’d try.
First off, do you have 2 hard drives inside your Mac? Hopefully, yes. If not, come back and tell us about your media drives.
Second, poke through the system prefrences to make sure that Final Cut is set to take advantage of that RAM. There’s a setting where you can allow it only take advntage of some of the RAM. Max that out and make sure no other programs are running, too. Re-set your Mac after you do this step to make sure everything’s cleard up.
Once you’re back, make sure the video is rendered. After you render the video, then select SEQUENCES>RENDER ONLY>MIXDOWN
Then export a quicktime movie to that second hard drive inside your Mac. (FILE>EXPORT>QUICKTIME) Set it to “Current Settings” and make sure “Self Contained” is checked on.
Then close your project and open up that exported file in Final Cut. (It will just float in a window…project-less.) Now try your print-to-video and see if you have any better luck.