If it is voltage, electronic or sensor/solenoid, you may not have to extract the transmission. Cross your fingers.
Anything internal requiring removing the transaxle,
I would suggest that you rebuild it with, or buy one that uses the best components you can get. I've seen so many " domestic" transmissions fail between 30-40K on the clock it is pathetic.
Do some research online. Some transmissions have had 3 or more generations of re-design, volumes of TSB's, reformulated fluids, and still, they may have components that are prone to premature failure. Some high-end aftermarket manufacturers use seals, materials that are specifically designed to remedy design/component materials, seals, and other key problematic OEM components. It is worth the time and effort to educate yourself. Good materials and components may seem high priced, but you may stay on the road and out of the shop for the life of your vehicle.
If its any consolation, at least, unlike the price gouging at the gas pump, you will get your moneys worth. And most likely a better warranty.