My modified method to doing this:
Remove rear tranny crossmember nuts and jack it up and shim under the mount to keep it up. Remove the pan and catch every drop of fluid. Clean and wash the pan, then reinstall. Lower the transmission and reinstall nuts for crossmember mount. Then measure the fluid you removed. Jack up the passenger side of the truck a few inches and pump in the fill hole the exact amount of new fluid that you got out with the old fluid. Example 5qts, 8oz. That is what you put back in.
Done. Here is my thoughts, if the factory filled it correctly, then this method will work. No need for the complex fill method. If the tranny wont take it and it overflows. Start it runs thru the gears a few times and try again. Mine took it all with no problems. I used about 5 and 3/4 qts. In not sure you would techically need to change the pan. Mine had 190k and was not good, but yours is only at 70k.