R. Ephraim Kanarfogel, Peering Through the Lattices: Mystical, Magical, and Pietistic Dimensions in the Tosafist Period, pp. 166-167, 168, 186 (some footnotes omitted):
Rabbenu Tam, the greatest of the early tosafists, has been characterized as a rationalist. Like Rashbam, Rabbenu Tam interpreted talmudic passages in ways that eliminated the roles of superstition and shedim, which had been left intact by Rashi and other predecessors. Moreover, Rabbenu Tam was unswervingly talmudocentric. He was not even inclined, as Rashbam was, toward the study and interpretation of Scripture as a distinct discipline.UPDATE: I e-mailed R. Kanarfogel and asked about Rabbenu Tam's grammatical work and commentary on the book of Job. Don't they show interest in non-talmudic topics? Or does he assume that these were not sustained interests? He responded as follows (posted with permission):
There are only a handful of passages in Rabbenu Tam's substantial corpus which, as far as I can determine, reflect mystical considerations, but their implications must be considered carefully...
Beginning in the middle of the twelfth century, R. Samuel b. Qalonymus he-Hasid of Spires and his son, R. Judah he-Hasid (followed by the latter's student, R. Eleazar of Worms), rejuvenated and greatly expanded (to include a highly developed theosophy) the mystical teachings and expressions of hasidut they had received from their Pietist ancestors and teachers who studied almost exclusively in Mainz. Perhaps the relative lack of interest in torat ha-sod shown by Rashbam, Raban, and Rabbenu Tam--despite their clear awareness of this material--was because the methodology of the academy at Worms in the last part of the eleventh century adumbrates and, through R. Meir b. Samuel (The father of Rashbam and Rabbenu Tam) and others, helped stimulate the development of tosafist dialectic. The influence of Worms, where mystical teachings were not in evidence, was dominant at the beginning of the tosafist period.
See, e.g., Urbach, Ba'alei ha-Tosafot, 1:70-71, 88-93; Grossman, Hakhmei Ashkenaz ha-Rishonim, 94-95...
 See, e.g., Rashi, Menahot 32b, s.v. sakkanah; Tosafot Menahot 32b, s.v. sakkanah; and R. Yeroham b. Meshullam, Toledot Adam ve-Havvah (Venice, 1553), sec. 21, pt. 7 (fol. 179c). As opposed to Rashi, who itnerpreted the talmudic dictum that a misplaced mezuzah was harmful because it could not serve to eliminate shedim, Rabbenu Tam saw the potential harm merely as the risk of injury if one bumped into the mezuzah because of its poor placement. Cf. Teshuvot R. Meir mi-Rothenburg (Cremona, 1557), #108, and Daniel Sperber, Minhagei Yisra'el, vol. 1 (Jerusalem, 1989), 46-56. As compared to Rashi (above, n. 45), Rabbenu Tam cites Otiyot de-R. Aqiva in purely halakhic contexts (i.e. only as a source for the technical writing of sifrei Torah), as does Rabiah, with no concern for its mystical implications. See Israel Ta-Shma, "Qavvim le-Ofiyyah shel Sifrut ha-Halakhah be-Ashkenaz ba-Me'ah ha-Yod Gimmel/ha-Yod Daled," 'Alei Sefer 4 (1977):26-27; Rabbenu Tam's Hilkhot [Tiqqun] Sefer Torah in Ginzei Yerushalayim, ed. S. A. Wertheimer, vol. 1 (Jerusalem, 1896), 97-99; Sefer Rabiah, ed. D. Deblitzky (Bnei Brak, 1976), 220 (sec. 1149); Sefer ha-Manhig, ed. Raphael, 2:587, 620; R. Samson b. Eliezer, Barukh She'amar, ed. M. M. Meshi-Zahav (Jerusalem, 1970), 74 (sec. 41), 101. Cf. Tosafot R. Elhanan to 'Avodah Zarah 28b, s.v. shoryeinei de-'eina, and above, ch. 2, n. 67. [Not also the differences between Rabbenu Tam and R. Judah he-Hasid in defining the thirteen attributes. See, e.g., Tosafot Rosh Hashanah 17b, s.v. ve-shalosh, and SHP, secs. 414-15; Sefer ha-Manhig, 1:277-78; J. Gellis, Tosafot ha-Shalem, vol. 10 (1969):124-35;...]
Your formulation about sustained interest is exactly correct. Indeed, at the point in the book where I offer this assessment, the footnote on that very sentence refers the reader to an (earlier) article of mine on the study of Bible in medieval Ashkenaz. There I specifically note both the dikduk work (and the way that it was received in Provence), and the perush to Iyyov, as well as Rabbenu Tam's statements about the study of mikra recorded in Tosafot in Kiddushin and 'Avodah Zarah (and other related references), all of which support the contention in the book that certainly as compared to Rashbam (and Rashi for that matter), Rabbenu Tam's interest was not a sustained one (except, of course, in the context or through the prism of talmudic/rabbinic studies). This last point is reflected in my statement that Rabbenu Tam was essentially 'talmudocentric'. My larger argument in this part of the book as you may know is that both Rashbam and Rabbenu Tam play down the mystical impulses of the pre-Crusade Ashkenaz of which they were aware. Rabbenu Tam also plays down the pre-Crusade involvement with parshanut ha-mikra as a distinct discipline (noted fully by Avraham Grossman), while Rashbam (obviously) does not.Note that I did, in fact, cut off footnote 87 where R. Kanarfogel references his article on the subject. My mistake.
I should also note that in the seven years or so since Peering first appeared (pun partly intended), I've come across some additional factors that are worth mentioning in this regard. As I will discuss in my forthcoming book, The Intellectual History of Ashkenazic Jewry: New Perspectives, there are few comments attributed to Rabbenu Tam in the corpus of the so-called Ba'alei ha-Tosafot 'al ha-Torah (found both in print and in mss.) that are not either sugya related or specifically offered in the context of talmudic analyses of Scripture. Quite a number of exegetical comments attributed to Rabbenu Tam in these works can be shown to be those of his student R. Jacob (Tam) of Orleans, who like his contemporaries (and fellow students of Rabbenu Tam, R. Yom Tov of Joigny and R. Joseph of Orleans= R. Yosef Bekhor Shor) did offer comments/critiques on pesukim (and on Rashi's perush on the Torah) that are essentially exegetical, and not just a reflection of talmudic approaches. (A good example here would also be ms. Paris 167 which has been characterized as a perush of RT 'al ha-Torah--although he was probably not the actual author, and indeed, is mentioned by name only around 15 times. This perush consists of talmudic Tosafot-like or Shas material on the Torah, not an exegetical perush 'al ha-Torah.) The same is true, of course, for the several Tosafot that cite RT on biblical verses--he knows Tanakh by heart and is very interested in undertanding the pesukim in question, but does so fundamentally through the prism of talmudic or rabbinic interpretation--there's no theory of peshuto shel mikra or 'omeq peshuto shel mikra that Rashi and Rashbam developed and continued (although Rashi and Rashbam themsevles obviously related to rabbinic/talmudic exegesis in different ways in their biblical commentaries.)
In addition, the several perushim on Iyyov that we have from medieval Ashkenaz in the mid-twelfth century, including those of Rashbam and Rabbenu Tam, may have been undertaken precisely by these 'rationalists' who did not involve themselves in mystical or magical issues (as other, mostly later Tosafists did, as I show throughout Peering) to convery issues of sprituality/Jewish thought. In Rashbam's case, his many other biblical commentaries are reflections of his deep interest in parshanut ha-mikra as well. For Rabbenu Tam, however, the one commentary that we have (at least to this point) can be seen as an expression of these other disciplines as much as mikra per se. And finally, a colleague of mine in J-m has suggested--but hasn't published it yet--that the grammatical work of Rabbenu Tam may not have been written by him. This, of course, is still speculative, but it joins the many other sources mentioned and referred to here and in my writings noted above.
So, to repeat (and sorry for such a long answer to a short question), your formulation is correct. I've kind of dashed this off because it is erev Shabbos. If any further clarification is required, please let me know.