1991 3k gt SL 4 speed tranny

hi I was wondering if anyone knows this, my car 1991 3000gt sl had a 4 speed tranny but it now needs to be replaced, the onlyone that I can find is a 5 speed tranny, my question is if it will fit my car , and also if it will not affect the tranny computer, and last if it will need a shifter change to a 5 speed

thanks hope someone can help this silly newbie