At one point there was a TSB for incorrect speedo, leading to recalibration and/or replacement of the gauge cluster. On vehicles with an analog speedo, it is indeed common for the speed displayed to vary from "actual"/OBD speed, increasing with speed. So at 60 mph, it might be 2 mph off, for example.
TSB 10-18-07 - SPEEDOMETER INDICATOR NEEDLE STICKING OR INACCURATE - BUILT ON OR BEFORE 3/25/2010