Pathfinder needles not working properly

Hi, I needed to change my speedometer from Kph to Mph so I just replace the "sticker" in Kph for one in mph. To do so I had to remove needles from speedometer and when I finished everything was fine. I took my car for a ride (in the city) no more than 30 mph and everything was fine. Next time I used the car I took the motorway and when I reached 40mph the needle did a weird movement and didn´t pass 40mph and went back to lower speed. Needle was working very odd, sometimes 0mph whilst driving but after a few minutes speed below 40mph was fine again but if you go again to 40mph or higher same story happened. What would it be, please?