Why does Rashi give exactly the same commentary about Girgashi in Shemoth 33:2 and 34:11 ? Truly yours.
In the classic commentaries on Rashi, I found no explanation for the repetition.. However, in the Likutei Sichot on Parshat Ki Tisa, the Lubavitcher Rebbe, Rav Menachem Mendel Schneerson zt"l made the following hairsplitting distinction. He claims that the leaving of the Girgashi as explained in the first Rashi took place after the expulsion of the other nations. This is understood by the letter "vav" והגרגשי"–"ve'hagirgashi" which indicates that it took place only after the other action. Meaning Rashi says that six nations were expelled and then when it came to the Girgashi , they were not expelled since they decided to leave on their own. While in the second Rashi the word used is "ki"- כי –"ki hagirgashi" = "because" which indicates that the leaving of the Girgashi had taken place earlier. In other words Rashi explains why are there only six nations mentioned. It is because the Girgashi had already left earlier and therefore now there are only six nations. The Lubavitcher Rebbe further explains that should you ask then so when did the Girgashi actually leave before the other nations or afterwards? His answer is that this poses no difficulty. The majority of them left before the other nations, while a minority left after the other nations. It should be added that the Talmud Yerushalmi Shvi'it (Chap. 6) says that since the Girgashi left without any contention with Bne yisrael they received the land of Africa.