extremely long time to load a page - 130 second

[kcm]

hi,

recently i just migrate+upgrade vbulletin to 4.1.4 patch 2 on my forum. but i don't know which one cause my forum to load slowly. (Page Generation 130.26436 seconds Memory Usage 5,589KB Queries Executed 11! -without login on index page)

but strangely, i've try with my 3 different computer and browser, but 1 from 3 computer is accessing with less 1 second to generate a page. but even the page load more faster, but it slow down when i try to post a thread.

can i anyone tell me where the problem is, i don't thing i should have a lot of tuning on the server, since this is not very high traffic forum.

i've tried:
- disable all plugin
- doing # top (but there's no memory issues)
- using two memcached server
- optimize mysql

server spec:
- 8G RAM
- quad core
- php 5.3.6
- mysql 5.5

forum:
- 40K members
- 675K posts

*yes, i did google, but with no luck*

thanks