From what you're describing, I think I may be having a similar issue after I recently had my transmission replaced, and all, on my 2012 PPV. Somehow, after driving in heavy rain on the highway, water mysteriously got in the transmission and, of course, the gunk screwed up everything. Anyway, if I'm stopped and in R or D, I press the gas pedal and there is a brief moment when the engine revs up. This is followed with a nudge as it moves forward or backward. This nudge is as if it was in neutral, and I rev up the engine, then suddenly shift it into R or D. My trusted mechanic told me is this is happening because the CPU needs time to adapt to the new transmission or I guess what others say 'relearn' one's driving habits. So basically, I have to treat it as if I am breaking it in like a new vehicle. But, stupid me, there was an instance on the day I got it back where I gunned the engine to pass a dumbass slow driver on a 2 lane road and then the day after I gunned it to beat a yellow light, and so the transmission started acting up with the nudging when either backing up or moving forward. I let it sit for a few days and when I drove it again, this time, I took it very very easy driving around. It's been about 2 weeks since getting it back, logging over 100 miles, and now it happens periodically. Of the times it happens is when I'm in heavy traffic and have to break suddenly which causes the transmission to downshift rapidly. Then, I get the nudge when moving from a dead stop. But then, it doesn't do it after slowly stopping. Anyhoo, I'm just gonna keep driving it very easy and hope this nudging will finally go away to the point where I can drive it normally and not worry about the nudging. Will see.
