Moving from Dexron 3 to 3309 oil in my Transmission

[Namo]

Hello guys, I have been using the Dexron 3 in my 2002 volvo s60 NA with 140,000 on the clock for about 4 months. I was recently informed that Dexron 3 would cause harm to my Transmission and mobil 3309 or or Toyota T-IV. So now I would like to move to the recommended oil. How do I go about this? Can I just do a drain and fill using the new recommended oil?

[vtl]

Drain and fill a few times, it takes about 3 liters per round.

Dexron III misses friction modifiers, it causes harsh gear shifts and erratic controlled slip. It could be your ATF it Dex-III compatible, but also has a modifiers pack that makes it compatible with modern transmissions, like AW55. You would notice for sure if ATF has no friction modifiers.