Transmission question...

I've noticed as its gotten colder here (not real cold, just in the 40s and 50s) that when the Xterra is cold it doesn't go into lockup in overdrive until the temp gage it close to running temp. I leave work, and pretty much get right on the interstate and have to drive 4 or 5 miles then all of a sudden the transmission goes into lockup. Anyone else notice anything like this?

The transmission is programmed that way. The reasoning for the programming is either to help warm the cats faster, warm the transmission fluid faster, or a combination of the two. Well, those are common reasons why other manufacturers program the transmissions that way but I don't know specifically why Nissan does it. It's normal behavior either way.