I have noticed this problem for quite some time. I am not really concerned about it, just wanna know what it is.

Sometimes, at low speeds, (20-30 kph), i'll release the throttle, and use brake or whatnot, maybe come to a 5 mph stop, then i'll give it some gas, to speed up again. Sometimes it does not respond, for a very brief moment (very brief) then the car will seem to shift into gear, jerk, and go.
This is of no concern, and happens very rarly, its not ruining performance, just a minor annoyance. Been like that since i got it.

Is it normal? Or common in these trannys?

does it sound like maybe the car is trying to start out in second? or does it rev up, and then catch like it is slipping?

Vacuum modulator played with low trans pressure. The low trans pressure shouldn't be a worry unless you have trouble shifting or slow engagements with the gear selector [such as putting the car in drive then waiting a second then you feel it engaging.. engaging... engaged]. It'* hard to explain, but it'* quite obvious. It'* also a harsh engagement.

The only thing you can really do is watch it.