check what you already have, mine came with a 1 tonner already in it. dunno why, either the '03 2500's lucked out, or it's my towing package, dunno, but i'd check first, my tranny has held for all 135k miles, heavy towing, mud riding, hauling, hauling arse, you name it, this truck has been through it, a few times.
i keep the tranny fluid 20k miles fresh, and don't let the cooler get too bug clogged.
to the OP, come off the fence and do the efan
a well wired one will work a lot better than your stock clutch fan
low temp tstat will give you the head start you'll appreciate on a triple degree day
the stock pump is more than sufficient
take it from the rest of us, our recipe works, especially on my heavy truck
i towed 14k lbs over an hour in 90* and never broke the halfway mark uphills