Um, yeah. I assume you went from 31" tires (stock) to tires that probably measure around 34". That's almost 10% difference. So, whatever your speedometer says now, add 10% to that to get your true speed. And your odometer is off also.
If your tires were smaller than that stock, then obviously it's a bigger change.
You need the ProCal and/or a new speedo gear depending on your model year..