Hi Sid, mines auto and yes when you accelerate on take off with a bit of urge you can feel it, and as I don't have a towbar I couldn't tell you if its any worse. Mine only had 150km or so on it when I noticed it, and its now got 11000km not getting any worse. Hey Sid just out of curiosity have you checked the level of the oil in the rear diff as Mine was way down from day one.
But I do remember back in 2008 or so, my then 1 year old 2wd Hilux 4.0 v6 auto developed the exact same vibration my Triton has had since new, any way cut all the bull shit out, took the Hilux in to the dealer where I always had it serviced, one of the Techos I trusted came for a run, done a few hard take offs from a standing start he felt it through the seat, went back he ordered a NEW CENTRE BEARING unit for the two piece tail shaft, few days later in it went, NO more vibration.
And yes when I moved house I had a trailer on loaded up and the vibration on take off was so much more pronounced.