Transmission seems to shift from second to first too late?

I asked this question about a couple of weeks ago, but I'm getting a 404 page error when I try to access the question again. While driving my in-laws Acadia, the transmission seems to downshift from 2nd to 1st too late. The shift is pretty noticeable, and the transmission was replaced about 2 years ago. Any help? I also noticed the engine seemed to almost stall while at a light. The engine rpms seemed to drop and then kick back up as if the engine was dozing off and then forced itself awake. Finally, the throttle seemed to be almost unresponsive once I got up to about 25 mph after launch from that same stop light. The latter issue could just be the natural sluggishness of the engine though. Thanks.