Originally Posted by blazzin1
Either way, it is an adjustment of the factory settings on the ECM, which in turn = loss of powertrain warranty in most cases (ask you local dealership to be sure).
I had my gears swapped on my 12' 5.0 with the speedo calibrated at the dealer and no effect on warranty. If I calibrated on my own using an SCT tuner for example, they may have had an issue with that since it involved a reflash.
I don't see how calibrating your a speedo would have an effect on your powertrain especially with a device specifically designed to calibrate the speedo only.