I have a 2018 2X4 LT eAssist (355hp) Silverado and just passed 3,200 miles. Purchased in June 2018. I have noticed the "bumpy" sort of surging when backing up as well. It is intermittent and because of other comments I knew to expect it. I also notice drive line "clunking" as well from time to time when shifting from Park to Reverse or Reverse to Drive. Not a hard clunk but.....noticeable.
Gas mileage has been interesting. We drive around the city most of the time (San Francisco) and if we use a whole tank of gas on city driving only.....we get about 14mpg on average. Not what I expected with an eAssist. However....if we go on a long drive (SF to Tahoe and back) we get about 24-27mpg and that is a big improvement over my 2003 Silverado I replaced.
I think the majority of fuel savings for me is the eAssist motor kicking in to assist and keep the active fuel management in V4 mode for longer time (or preventing V8 mode shift return altogether under light acceleration) when on the free way.
I love the truck, huge improvement over the 2003 LS and kids dig the extra room with the crew cab. Enjoy the thread as well. Keep the comments/updates/experience coming.