Does this seem normal? Server acting real slow.

Well, I want to be as descriptive as possible, so let's see.

Server was purchased in January 2007.

Dual Core 2.60Ghz
1gb of memory
Red Hat Fedora Core release 4.

Posting Activity Statistics:
January 2007 - 8652 new posts
February 2007 - 9028 new posts
March 2007 - 14170 new posts
April 2007 - 13485 new posts
May 2007 - 12194 new posts

Average about 175-200 users visiting per 24 hour period.
At most 30-40 registered users online at once.

Currently Active Users: 37 (17 members, 20 guests)
Forum Home:
Page generated in 1.5782 seconds (53.45% PHP, 46.55% MySQL) with 28 queries
Server Load: 6.80, 6.09, 5.25

It ran really snappy for the first few months. In May, my server was hacked and the hacker gained access to FTP and uploaded a Bank of America phishing site. I didn't realize this, just thought the password was compromised and reset the password. Site got shut down a week later and found out that the phishing site was uploaded. Because of this, I I had contacted PlatinumServerManagement and had them lock the server down, get rid of vulnerabilities, etc. They also tweaked a lot of settings and optimized a lot of the server functions.

Well, a couple months later and my server sucks. I have had to do graceful restarts every 2 weeks because the server load gets so high and lags so bad. For instance, right now the uptime has only been 5 days, 22 hours, and 27 minutes.

phpSysInfo says that my physical memory is 93% used.
But, when I go to WHM and go to the Service Status, it says 51% used.
Then when I click on Server Information, it says Memory: 1000512k/1015744k available... that's like 98% available. WTF?

In any case, for what my server's statistics are compared to the users online at one time and average number of posts, etc, doesn't it seem like something is missing? I thought when I leased this dual core 2.6ghz 1gb server that I was going way above what was necessary so that it would last a long time... it's only been 6 months and now I'm wondering if I didn't get enough?

Any constructive input is appreciated.