Does your overdrive button work at all? Mine stop working, It was in overdrive all the time and now and then the button would work and could take it out of overdrive... Yeah it what we thinking what it was doing... Playing with the button now, You can see the pin with the plate going for over the place when you push the button in and out.
I know with mine, the faster you went, the wrost it got. It sould like you got the same stutter as me...
What happens when it starts to stutter and you take it out of overdrive and then put in back in? With mine when the overdrive button worked, It would stop for a while and then would start away.
Would take the overbutton out and see how the pin moving around when you push it in and out and also take it apart and clean it, Clean mine few times and it did work of abit. Also take the gear lever out and check to the wines for the overdrive to see if they are not broken ect
I know mine off trademe. they are hard to find... But try trademe and the nissan place in chch...