I am having a very similar, if not the exact same, problem.
I just got the evo shift and updated it to GB. All I have done so far is log into my google account. I have not downloaded a single thing. When I go to Settings > SD & phone storage it says that "Internal storage" is at 343 MB. To further show that this is storage not RAM i go to Settings > Applications > Manage Applications > All and I see "85MB used" and "346MB free".
Now as most of you should know, sprint advertises the evo shift to come with "2GB Internal Storage". I will be quite shocked if the OS is taking up around 1.5 gb of that internal memory.
Is anybody else having this problem? Is there perhaps something going on with the phone (a misreading, or something faulty).
I'm aware sd cards can help alleviate this, but 346MB? Really?
Also, to make sure this is not the RAM it is reflecting I killed a few applications like Voicemail and what not and watched the RAM display change but the "346MB free" internal storage remain the same.