(This post should not be in the Internet Marketing forum, but I am willing to offer some advice.)
Is it your own website? Do you think it has been hacked? Google's diagnostics tool might turn up some problems, but it might miss others. If it really has been hacked, you might need more thorough measures to detect it and fix the problem.
In the following URL, replace example.com with the domain of the site you want to test:
This test is pretty good. There are other, free, online test sites you could try too, if you want more than one opinion.
You can easily take a look at the specific items and how long they are taking to download by using your browser's developer's tools. for example, Chrome has the ability as well as IE v9 (hit F12), and even Firefox.