Inox222

So i was sitting at a light the other day and went to shift into first when the light turned green and couldn't get it into gear, tried all the gears and none of them would go in. First tried pumping the clutch but that didn't work either. It wouldn't grind or anything when trying to push it into gear just wouldn't go in. Finally i shifted the transfer case into nuetral and bam when right into gear, shifted the transfer case back into 2 hi and took off but as soon as I tried to shift into second it wouldn't go again. Ended up doing the process again but putting it in second and driving home in second. When I got home turned off the truck then turned it back on and the problem was gone. The transmission is worn and makes some noise in 2nd and 3rd, so it does need to be rebuilt. Once in awhile it will pop out of first as well. Anyone have any ideas what it could be. I don't want to replace the transmission and it end up being the transfer case was the culprit. I did change the transmission oil couple months ago but have not done the transfer case oil yet. Any ideas?