Here it is called Timnas Serach. Why is it called Timnas Cheres in Shoftim (2:9)?
Rashi: They put an illustration of the sun on his grave, to show that he stopped the sun (Iyov 9:7) "ha'Omer la'Cheres v'Lo Yizrach" (Bereishis Rabsi Chayei Sarah 100b). People who pass by his grave say 'woe to the one who did such a great matter, and died!
Rashi citing Bava Basra 122b: Really, its name is Timnas Cheres. It is called here Timnas Serach because its Peros are so fat that they are Masri'ach (spoil). 1
Radak: We find words in which sometimes the order of the letters is switched, e.g. Keves and Kesev.
122b: Some say that initially (before Yehoshua received it), its Peros were [dry] like Cheres (earthenware), and after [Yehoshua received it], they spoil. Some say that initially its Peros spoiled, and after [he received it], they were like Cheres (did not spoil).
We do not find a place called Har Ga'ash!