Purchased my first jeep on saturday. No knowledge on service history so I want to change all the fluids( will have to be one at a time for budget reasons).

It's a 95 SE 4.0L.

Have the oil filter ordered (PL30001).

Looking for the best detergent oil for the engine. Where I live; it is almost -30 tonight. I grew up in Florida; and used Shell RotellaT 15w-40 in winter and Valvoline VR1 20-50 in summer. Occasionally used Mobil1 to clean out a new used car or truck. Wondering what oil will best clean out the engine?

My usual combo for cleaning would be 4 parts oil and 1 part marvel mystery oil or seafoam and a new top end filter for 1-2 weeks then switch back to regular oil...

Second step will be differential....Again temperature range from -45 to 90 degrees...what would be best oil?

This may be a dumb question but I am guessing that the front and rear differentials and transfer case all use the same lubricants and should/need to all be changed at the same time? Or is the transfer case filled with a different fluid like tranny fluid?