Transmission and Differential Oil Change

I used a gallon of Mag1 80W-90 High Performance Gear Oil (API GL-5 and MT-1, MACK GO-J, SAE J2360, Limited Slip) for both the transmission and differential, since there was whining in the transmission after a long high speed drive on the highway. The old transmission oil still looked clear although the viscosity looked degraded and much thinner.

There was a bit of water mixed into the differential oil (oil looked a bit muddy). I suspect some water had entered into the differential housing through the breather while I was driving in the rain. Good thing I got to replace the differential oil as well for peace of mind.

After the changing the oil, there was still that whining sound, but the drive was definitely much smoother. I also noticed smoother shifting especially from 2nd gear to 1st. Before I'd have to "punch" into the 1st gear slot, but now there's much less effort needed.