Switching to Amsoil 0-40 for my engine oïl tonight. Now wondering what to use for my trans and diffs. Manual says 75W-140 for trans and rear diff and 75W-90 for the front. What do you guys suggest running for this? I have eassy access to Royal Purple 75W-90/75W-140 Synthetic Gear Oil. Never really used RP so wondering what are the best options here.