Figured I would throw my 2 cents in here. I have an 18 power wagon and use it to tow my camper (probably around 11k). A typical trip is from 1100 ft about sea level to 7000 in an hour and a half. I camp year round so temps vary but the hemi has never got hot. Neither had the 6 speed (I know you would have the 8 speed). I would consider this to be somewhat extreme since I go pretty much straight up the mountains and the grades are all over the place. It gets about 9 mpg but I am on 33s with 410s. I would not hesitate to grab a gasser with 3.73s. I have an 06 cummins mega and my 18 is way more comfy and I am not staring at my pyro all the time.