You want to be careful with the synthetics, if you pick some up you have to make sure it is yellow metal friendly. Otherwise they will eat up the bronze in the transmission/transfer case.
I put some in my Tracker and it made the shifting worse, but my syncro's are a little worn and when I drained the oil out to switch back it was almost black. I think the synthetic went through and picked up all the garbage from 100+ miles of ownership. Hard to tell if it would shift smoother with putting syntetic back in as I don't feel like doing it.
A Sammy owner in my club users synthetic and loves it. Others here can probably chime in on their experiences with different oils in the transmission.