There is an obvious bottleneck.
Curl testing:

url_effective: http://PremiumDomains.US
http_code: 200
http_connect: 000
time_total: 11.360
time_namelookup: 0.004
time_connect: 0.144
time_appconnect: 0.000
time_pretransfer: 0.144
time_redirect: 0.000
time_starttransfer: 11.098
size_download: 21866
size_upload: 0
size_header: 437
size_request: 188
speed_download: 1924.000
speed_upload: 0.000
content_type: text/html; charset=utf-8
num_connects: 1
num_redirects: 0
redirect_url:
ftp_entry_path:
ssl_verify_result: 0
Critical point: time_starttransfer "The time, in seconds, it took from the start until the first byte was just about to be transferred. This includes time_pretransfer and also the time the server needed to calculate the result".

http://curl.haxx.se/docs/manpage.html

I would guess that there are too many clients connecting to that server. So it's running out of connections rather than resources like CPU or bandwidth. Just a guess.

Have you tuned your scripts ? For example a database lacking indexes could result in excessive load time.