fluids for towing?

Hey guys, what is everyones opinion on synthetics and additives when it comes to differentials, tranny, t/c? I've heard that the aw4 doesn't like synthetic tranny fluid, but what about the differentials, as I've known a lot of people that switch to synthetic diff. fluid when towing a lot. Also, I've seen a lot of additives recommended for use when towing a lot (from good brands like Lucas), has anyone used these and would recommend, or are they something to stay away from? Any advice would be much appreciated

Paul