Try a 50/50 mix of Lucas Oil additive and 80/90 wt gear oil to see if that helps. My old Duster 340-4spd was noisy on upshifts but that mix really quiet it down. It had ATF in it previously when I bought the car. Original 4-spd with 92,xxx miles and it never gave me any problems.

1970 FE5 Duster 360/904/3.91's SOLD 1973 TB3 SpaceDuster 340/4spd/4.10's SOLD Moparless for now but when the opportunity is right I'll have another one.