FCP X playback problem when updated to Lion

I am having playback problem in FCP X since I update to Lion.
I transcode my material to ProRes and I also crated proxy but I still have the playback problem.
I didn't have this problem with Mac OS X 10.6.8 Snow Leopard
What can I do:
Should I change my NVIDIA GeForce GT 120 to ATI Radeon HD 5870
Should I add more RAM from 12GB to 32GB
What can I do please help.

My Computer:
Mac Pro (Early 2009)
2 x 2.93 Quad-Core intel Xeon
12 GB Ram
NVIDIA GeForce GT 120
OS X 10.7.4 Lion
FCP X 10.0.5
Drive G-Technology G-Speed es pro Raid 5 with 2.7 TB Free

Clean installs typically resolve most problems resulting from updates to either FCPX or OS X.

Uninstall FCPX using an app like CleanMyMac, AppZapper, or AppCleaner. Don't just drag the app to the trash, you may also need to kill preference files.

Download FCPX again from the Mac App Store

Also, make sure you are running FCPX 10.0.5 with OSX 10.7.4

Please explain the playback problem. Also your complete workflow.

Digital Rebellion makes a free app called "Final Cut Remover" that covers Final Cut Studio apps, Final Cut Server, and the new FCPX/Motion/Compressor apps.

But I'd too like to know your current hardware specs first.

My Computer:
Mac Pro (Early 2009)
2 x 2.93 Quad-Core intel Xeon
12 GB Ram
NVIDIA GeForce GT 120
OS X 10.7.4 Lion
FCP X 10.0.5
Drive G-Technology G-Speed es pro Raid 5 with 2.7 TB Free
AJA LHI

BenB you mention Final Cut Remover, I have the app should I select delete all (Application, preferences, content, receipts).
Should I back up the free plug-in that I have downloaded.
Should I back up anything else.

Thanks to all for the help.
Ricky Dominguez

What is the playback problem? Resolution/Codecs are you working with?

For example Canon MXF Footage will strobe badly in FCP X if you don't have High Quality selected in preferences.

The playback problem is that it's is drooping frame, the time in the dashboard it slow and skip frames, the material looks like it have a strobe FX. When I export the video as ProRes it's look perfect in quicktime, so it's a problem inside FCP X.

I am editing 3 TV spot 1 x 30ss 2 x 15ss , the material was recorder with Canon 5D 1920x1080 29.97p, I begin editing with FCP X 10.0.5 in Snow Leopard Mac OS X 10.6.8 with the original material but it was kind of hard for the machine so then I convert the material to ProRes and the material play perfect. The past thursday june 28 I purchase Lion because I want to istall the latest version of AJA software so I have broadcast monitor and it require Lion. Friday I edited a 720x486 project with no playback problem, Yesterday I return to my 1920x1080 29.97p project and that's when I notice my playback problem. I try playback with high quality and better performance and also try proxy with same results.

Ok well then there is something not right. I'm on Lion and mostly always edit 5D footage without rendering or transcoding on a much older machine than yours. Have you deleted FCP X and re-installed it? Have you tried turning off the AJA outputting see if it's a driver issue?

I delete FCP X with Digital Rebellion FCS Remover, I re-install Lion an now I am downloading FCP X to install again. Then I will try turning off AJA or even butter delete AJA and re-install.
Thanks Seanus and the other for the help.

I will let you know what happen.