Painfully slow admin/dashboard, public site is fast

I have about 15 wordpress sites set up on a reseller hosting account. 2 of these are multisite installations, and on both, using the admin pages is extremely slow – sometimes slightly less painful, but always slow nonetheless. I’ve complained to my host and got this response:

“This slowdown is being caused by the loopback connections used by the scripts running on the admin page.

A loopback connection is when a script accesses a local script by going out through the internet. These are prohibited on our systems, which is why they are timing out (and causing the site to run slowly).

The scripts should access the files through the local file system instead.

You’ll either need to disable the loopback connections somehow, or disable WordPress components until this stops happening – then you’ll have identified which component is causing this problem.”

the thing is, the MU site I’ve allowed them access to, and have been disabling themes and plugins in to try fix the problem, is still very slow despite the fact that now the only plugins and themes installed are things i KNOW work fine with my other wordpress installations:

Arras Theme
Magazine Basic
default wordpress themes

.html on pages
Akismet
Google Analytics for WordPress
NextGENGallery
WP Super Cache
Youtube Brackets

that’s literally it. Any ideas what I can do then to fix this issue?