What i`ve found (after owning 3 of the 8-speed 8HP70 transmissions in the 1500 RAM), i traced it down to the torque converter unlocking VERY late in its programming, in MOST cases, and its mostly noticed after a full complete stop....THUMP!!! When i use the +/- gear selector, dropped down into 8th gear, no more THUMP when i stop. Once i`ve hit the +/- back into "D" mode, i can repeat the THUMP at every stop. I haven't tried TOW/HAUL mode because i see no need to. But if some of you fella`s wanna try it, go for it and report back here to let us know what happens when you tried it. I will bet that in TOW/HAUL mode, its going to do the same UN-THUMP as the +/- method i tried. I believe the TOW/HAUL mode, when used, it partially unlocks the torque converter. I wont say this will work for everybody, its just some things i`ve been trying after owning 3 of these RAM1500 trucks with the 8HP70 transmissions.
Those that know the 8HP70 transmissions inside and out, know, that chrysler designed the software to keep the torque converters locked up for as long as possible, for efficiency & mpg reasons. Until chrysler re-write`s the software for the RAM from 2013 to 2018, 8-speeds, or comes up with a flash update to unlock these torque converters sooner, rather than later, this THUMPING issue will NEVER completely go away. I now own a brand new 2018 sport, it thumped for the first 500 miles, it has decreased since new, but i can make a severe thump happen, by coming to a VERY aggressive stop. Whats happening there is, the suspension/driveline is loading against the transmission as it slams the gears down into lower gearing.
When you drive a BMW that has the ZF 8HP transmission, there is NO THUMP whatsoever... its chryslers programming causing this little demon thumping.
PS: those that keep beating the dead horse of the gas tank thumping, thats a different horse of a different color, its NOT the same issue as the transmission 2-1 thump.
That theory HAS BEEN debunked, and several times, on many different RAM truck forums.