Regardless of brand or weight I think synthetic is a good idea. My dad says his car is more consistent since he put synthetic in his dana 60(first run is not the slowest anymore).

My jeep has locking differentials in both ends. I could tell a big difference in how they act when I went to synthetic gear oil. If it makes a difference in something like that it has to be better for the gears as well. I don't buy the high dollar stuff, just the cheapest synthetic the parts store has on the shelf.