Why not replace existing receptacles with GFCI receptacles rather than play with the range wire?

"the existing wire looks like a 10/3 cable formerly from a range possibly?"
I doubt it. If you plan to use that cable, determine precisely the wire gauge as the first step. 10 gauge solid is 0.102" diameter, 12 gauge solid is 0.081 diameter.

Are you sure that wire is 10/3? Before 2005, kitchen countertop outlets were wired with 14/3 fed with a double pole breaker, so you'd have the top and bottom of the receptacle on separate circuits. There is a tab that goes between the two brass screws that you needed to clip off, but you'd leave it on the silver colored screws.

However, unless you really need a GFCI in that location, I personally would leave it as it is, or splurge for a double pole 15 amp GFCI breaker (they are pricey)if the new code allows it. You would basically be replacing two 15-amp circuits with one 20-amp circuit, and depending what you used to plug in at that location, you may no longer be able to do so. For instance, you no longer will be able to use your 1200 watt toaster while your 1400 watt coffee maker is in use.

I should have mentioned that what I said only applies to Canadian kitchens. My mistake.

It does appear that disciple.07 is in Canada. I know the NEC as it applies in the USA. So this thread is not for me.