Also, I haven't read through the whole thread, so this may have already been mentioned, but getting an MA or PhD in Japanese doesn't just mean you take higher-level language courses. The so-called "grad-level language courses" mentioned in another thread are actually usually more like bibliography courses, teaching you how to locate information you need for your research using scholarly reference works, not actual language courses. As such, they're usually not open to undergrads, because they serve a very specific purpose. Most MA programs will also require a Master's thesis in addition to the coursework and language in order to graduate, so you can't just take some higher level courses during your BA and finish up with an MA too. Even if they don't require a thesis, they will probably offer a thesis option, which you should take if you have any intention of pursuing a PhD.
You have to do significant original research in your field (in Japanese studies, this could be history, linguistics, art history, literature, etc.) and write a book-length dissertation in order to get a PhD. The language itself is practically secondary. Japanese is just a skill that allows you to do the research, not a goal in and of itself. And your level has to be high enough so that your language ability doesn't get in the way of doing your research, which will consist of reading original documents, scholarly papers, etc.
You'll also probably need to learn either Chinese or Korean, and maybe even Classical Chinese depending on your specialization. You'll likely even be required to learn French or German (or both). These other languages are all for the purpose of keeping up with research published in those languages. And even if you're not required to learn them by the faculty at your school, you ought to acquire reading skills in these languages anyway if you want to be able to compete with your colleagues. If you've missed out on a key piece of research in French that renders your current research project moot and everyone else has read it, you will not get published and you will fall behind the rest of your colleagues as far as your knowledge of the field.
Keep in mind, too, that you won't be likely to earn any credit toward your degree for these language classes, because they, like Japanese, are secondary to courses in research methodology, seminars, reading courses (not reading in Japanese, but reading research related to your chosen field, mostly in English – think 400 pages a week or more), etc. Any language courses you're required to take are for the purpose of making up for your deficiencies, and so will be on top of your full-time course load.
You will usually have two or three years from the start of your PhD to pass your language exams for all of these languages (in addition to fulfilling your course requirements), or else be put on academic probation. After passing your language exams, you will have 6-12 months to read 100-200 key books in your field (as determined by your professors) before taking a qualifying exam. This "qualifies" you to be able to actually stay in the program and begin your dissertation research (as opposed to *possibly* being given a consolation MA and being asked to leave the university). On top of all this you will be teaching undergrad classes and getting paid either nothing or very little. Once you qualify, you will spend a few years researching and writing the dissertation. Many people who make it this far drop out without finishing the dissertation, because it's just too damn hard to continue on, or find funding, or whatever the reason may be.
Altogether you're looking at 4 years of undergrad work and probably 8-10 years of grad work, depending on the program, your research, funding, and any number of other factors.
This isn't to dissuade you from pursuing a PhD. It's so you know what you're getting yourself into. You can prepare by taking a minor in Chinese, for example, and trying to learn to read French or German (reading knowledge is enough). Buy a book called "Getting What You Came For" by Robert Peters, and one called "Graduate Study for the 21st Century" by Gregory Semenza. If your undergrad school offers a senior thesis option, do it. I wouldn't recommend going to the same university for undergrad and grad school, you'll only get one set of approaches to the field. And if you do go to the same place for your BA and MA, go somewhere else at all costs.
And please don't blame your awkward English on being "Texan". They teach the same standard of English there as they do anywhere else in the US. And your English writing skills will have to be formidable in order to complete any higher education, or even be admitted.
