The gear change didn't affect your speedometer. The execitor ring still spins the same as before, it's attached to the ring gear so no change there.

 

My van is old and doesn't use an exciter ring. It just uses the old speed odometer cable and gear. I was looking into changing the speed odometer gear but that may be problematic as I believe the AOD has one gear built into the "output shaft?" Tail shaft?"

 

That's an easy fix. There's a plastic gear on the end of the speedo cable you can replace to fix this. You need a gear with one or two teeth more to adjust the speedometer. Mustangs Unlimited stocks them. The dealers used to stock them, but I don't think so now. The tailshaft has grooves cut into it that the gear engages. That can't be changed. The cable gear can.