Transmission and T-case fluid

So I have searched and looked at hundreds of threads but I can not determine the correct weight and type of gear lube for my T-14 tranny and my Dana 20 T-case. I believe they are the same and I believe the are GL-4. The service manual calls for 80w oil.

A few calls that I have made have told me that Royal Purple Syncromesh is what I need. I researched that and it seems correct. However, do I really need a $15 quart gear oil for a 35 year old Jeep. Help a guy out please.

Keep in mind that I live in Phoenix, AZ and that our outside temps are very mild. In fact the coldest I have seen when I have been awake is 35 degrees.

edit: to add oil weight recommended by service manual.

 

regular GL-4 oil can be found at any parts store. 75w90 or 110 should be fine. People have also ran 50w oil. You pretty much can't go wrong with whatever weight they have.

You dont need synthetic, but I've found it shifts better with it.

 

A t-14 would probably work on deap fryer oil from McDonalds. Pretty much any 80-90 weight gear lube will work. The t-14 is very stout, not really a high perfomance speed shifting trans so spending a lot of money on synthetic may be fruitless. I have seen many dana 20s running atf behind turbo 400s. They are pretty hard to kill also.