The above Info is correct, only the TCC Lockup needs power to work.
I just assumed you were calling the Lockup, OD/4th gear as some do.
It does sound like you may have a 2-4 Band or 2-4 Servo problem. You stated very fast 2-3 shift, now no OD/4th gear. 2nd & 4th gear use the same Band.
Converting it to a Carb requires the correct TV Cable Bracket and TV geometry corrector Bracket, if using an Aftermarket Carb such as Holley, Demon or Edelbrock for proper Line pressure rise. Correct TV cable setting is very important to prevent Trans damage.
What Rear gear ratio and Tire size do you have?