Manual G56 vs the Aisin.
Tow rating = how much trailer the truck can pull and has nothing to do with how much load the truck can carry.
Looking at the '13 2500 trucks with the 3.42 gears shows a 150-300 lb higher tow rating than the '13 3500 SRW trucks with the 3.42 gears.
You either need those big 9750 RAWR with the 3500 DRW for carrying 6k-7k payloads or you don't. Or you can choose a 3500 SRW truck with the smaller 7000 RAWR for 4k-4.5k payloads.
Ram for '13 has lots of different truck configurations with the Aisin/68RFE or the G56.
http://www.rambodybuilder.com/year.pdf