thinking about trading my 2019 6.7 and getting a 6.4 with a 8 speed. Wanna see if any of you guys are getting for mpg towing with a 6.4 and 6.7, ill be towing a sxs (x3 max on single axle trailer) weighing around 3-4k I would think a boat that wait will yield same results. Reason i ask is I will be storing my toy hauler during the season and evey other trip will just tow the sxs on single axle and swap trailers at storage. But if the mpg isn't worth it. I had a 09 2500hd with 6.0 6 speed and 4.56 gears and it was very thirsty and would get hot pulling 10k through the mountains.