Speedometer
 

I have a 99 ford E350, 7.3 diesel, 4R100 tranny. I replaced the tranny with a used one, same 4R100 with the exact same numbers on the tag. After the tranny swap the speedometer isn't reading correctly, For example the speedometer says I'm going 70mph in actuality I'm going 60mph. Above 50 there seems to be a ten mph difference. I replaced the speed sensor with no change.
What am I missing here?