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The problem is that when I start driving I spidometer stays at 0, and then at some point it “jumps” and shows real speed, in that moment the transmission shifts to next shift. Also I hear a lot of banging when shifting, so do you have any idea what is happening? One more thing, when I connect car to diagnostics I get g68 error. Sorry for my bad English

There is a TSB 01-07-09 for your vehicle covering the G68 speed sensor. A faulty connector wiring is apparently the problem. Go here and you can read about it yourself it also instructs you how to fix it. But at least it will give you some good information.