As for me they are not all the same. I 'have to go' is okay. (Right Grammar) It means I'm leaving now because I must do it. I've learnt that 'I have got to go' is wrong. Because we use 'have got' to mean we possess something like a house, a car, a sister. For example: I've got a sister/ I have a sister. I gotta go is 'slang'. Though, I know in spoken British English 'Have to' and 'Have got to' is the same.

"Get/got" is one of the weirdest words in English. I has no fewer than 28 definitions (see Dictionary.com). When the word "get" is used in a verb phrase, it can have hundreds of definitions based on its context. The most common uses of "get/got" is for the words "to be" or "to have" or "to obtain." There is never a sentence where you must use the word "got." When you can think of a choice between "got" and another word, always choose the other word. "Got" may be helpful for people learning English, but it may also be a linguistic crutch. Or it is simply poor language by native speakers.

'I've gotta go' is a shortened version of 'I have got to go', which both mean 'I have to go'. 'I have to go' is the proper way to say it, but for some reason, in English we use 'got' in many phrases. I, myself, am also confused by the use of this word. When people say 'I have got an apple', it means 'I have an apple'. I really don't understand it. English isn't a very clear language at times, even for native speakers. :(

they are the same meaning.....just different expression

They are all the same.