Any one have experience in their speedometer being inaccurate? I have a '66 Newport with original engine and transmission. I downloaded a speedometer app and if my speedometer reads 30 mph the app shows I'm going a few miles an hour slower. The faster I go the larger the gap. If the app says I'm going 55 the speedometer says 65. My buddy has a '67 Mercury Comet and he says his does the same. Were all speedometers this inaccurate back then?