If you pull the fuse or unplug the trans computer, can you shift manually with the shifter? If not, then you're looking at a mechanical problem. If it does then it's electrical.
Three possibilities here.
1. TPS is bad and telling the trans computer it's floored. This is easily tested with a meter. I would think you would have seen this prior to the swap.
2. The rear output speed sensor isn't working and the trans computer thinks you're not moving. The sensor itself should be the same between 2wd and 4wd. Not sure what you mean by the gear? You're talking about the VSS speed sensor?
3. Bad solenoid #2 solenoid or a bad rebuild.