Toyota Corolla Computer Replace/Remove

If I Swap Auto Trans From 3 Speed To 4 Speed With Overdrive, Is It Possible, Do I Need A New Ecu(computer)? What Else Are Involved I Have A...

I Have A 98 Toyota Corolla That Has A Misfire On Cylinder 3. I Put New Plugs In And That Plug Is As Clean As The Day I Put It In. I Do Have...