You need an online calculator to figure out the rest.
You need to be honest with your cruising speed.
3.23 X .80 = 2.56 final drive ratio.
With that math done, add in tire size and speed you want to travel at on the calculator. This will give you the RPM. For automatic transmission guys, converter slip not included but it maybe an option on the calculator. The known slip percentage of your converter is what?