Note: i group by conversation, if that makes a difference (though it shouldn't).
Here's what happens: When a certain thread gets to be more than 15 or so messages, a new email takes forever to load. As i showed you, the loading message thing appears for a good 2 minutes; at least. I don't know whether it keeps loading when the screen times out, so i'm often times tapping the phone to keep the screen awake until it loads. It does, however finally load, but what i've noticed is that the ENTIRE thread is encompassed within the email; meaning that i could scroll and scroll and see all the past emails.
This has to be an issue with either Google or Mail. I don't, however believe that there is a setting in gmail which truncates incoming email to only the text which is in reply; so the only solution i can surmise is that something has to be done about the way the mail app receives.
For anyone that looks at this, i've found the solution to be to add gmail as an exchange account, the way you would on an iOS device. It takes a little longer to get the sync going, but once that initial work is done, i haven't experienced another loading message, and as a byproduct, my battery life has significantly improved.