You do need a correct VSS signal for shifting of an electronically controlled transmission. It can often be calibrated electronically, but not always. If you have one of those gear driven electronic speed sensors, changing the speedo gears may still be a good approach. For a 700R-4, it just means lockup will happen at the wrong speeds. Also, for 80's trucks, the cruise control works by counting revolutions of the speedometer. The cruise will still work fine with the speedo calibrated incorrectly, but you do need a working speedo. Also don't forget that the odometer will be wrong when you're not calibrated. After swapping the whole drivetrain, the actual mileage isn't as relevant, but if you sell it'll have to be marked "not actual mileage".
There are also situations where a GPS speedo doesn't work - like a tunnel (or a dyno!). Also, if you shipped the vehicle cross country it could take a little while to get a fix. I understand they typically work quite well.
There are also situations where a GPS speedo doesn't work - like a tunnel (or a dyno!). Also, if you shipped the vehicle cross country it could take a little while to get a fix. I understand they typically work quite well.
