There are several threads on just this subject. Opinions, as you might expect, are many and varied. I used standard 5W30 in the engine for break in, then switched to Castrol Syntec 10W30. The T-5 box needs ATF, so I used
synthetic ATF right out of the box. The diff got filled with Mobil1
synthetic diff
oil + Ford friction modifier. With the locker, you can eliminate the friction modifier.
Have been using the synthetics for about 10 years now on other cars. The stuff just seems to work better, make parts last longer, stay cleaner, not form sludge from high temp coking, crank and roll easier in the winter. Can't say that any one brand of
synthetic is better than another. Marketing hype is marketing hype. Read the independent test results for comparison. Can say that synthetics are an improvement over petroleum based lubricants from personal experience.