[Rich-Tripower]

When we first got the GTO back together, we found that the speedometer read slow. Over the years the car had various sets of gears in the rear end so this wasn't a huge surprise. The car originally had 3.23 gears but we ended up with 3.55s. Anyway, based on which driven gear we had I did the math and determined which driven gear we needed, I changed the driven gear and everything was great. The speedometer was right on based on timing between mile markers and speed read through a GPS app on my phone.

However, when I got the GTO out for the first time this past weekend, the speedometer barely read at all at first, was really slow to react to changes in speed up or down and basically acted poorly. As the drive went on and things all got properly warmed up it got better, but still read about 5-10% slow. When speeding up or slowing down it occasionally appears to temporarily stick at 40 mph or so so something isn't right. No noise from the cable or anything and it has been properly greased. Would this be an issue of the speedometer itself and is there anything I can do myself to address the issue? It was clean when it went back in and I don't suppose you are supposed to lubricate anything in the speedometer but then I've never had much trouble with a speedometer. I could try cleaning and regreasing the cable, but I don't see how that would be the source of the problem.