Ford 8.8 swap?

I did this swap from a 7.25 to a 98 Explorer 8.8, in my 68 Dart. The 8.8 has 3.73 gears and the 7.25 had 3.23s. My speedometer was accurate at 60 mph before the swap. Now, in order to go 60, by gps the cars speedometer reads 84mph. I'm running 24 1/2"dia tires so the rpms are well above 3000.
The sticky 8.8 thread here explains everything youll need to do. Personaly, I think the gear ratio is to low and I'm going to re-gear it to 3.23. Either that or install an overdrive.