Using 50mph as an example your driveshaft (and transmission output shaft) is turning 14% slower with the 3.55 to run 50mph than it did with the 4.11. This means the speedometer drive gear on the output shaft is turning 14% slower affecting both the speedo and odometer. To speed the speedo drive back to the 4.11 speed you need a drive gear with more teeth or a driven gear with less. Usually you have to change the drive/driven gear as a set to get the percent reduction or increase one needs. We wait till the rear end choice is made and tire size selected then use the GPS to find the error and correct accordingly. google speedometer drive/driven gears and select from one of the many suppliers. Some have charts to plug in your gear and tire specs.
