I bought a new Dart Sport with a 4-speed in 1973 and the transmission was noisy. The dealer drained the ATF and refilled it with gear oil and the noise went away. I’ll never put ATF in a gearbox ever but that’s just my opinion.
I've always used 75w-90 gear oil, no complaints. But my brother-in-law had a stick shift Dodge Van with the trans filled with ATF. I could hear that trans whining from a block away.
