Does the shifter have to really be pushed to get to reverse and never really feel right? DO you have the air shift t-case or the older Sprag type?
The non air shift t-case has to know which direction the truck is going. If you by chance were sitting at a stop sign in 1st, let off the brake and rolled backward before you started going. You caused something called "wind up' in the drive train. Lift up a front wheel off the ground. Be very careful becuase it might start spinning on you. Once it is done spinning, put it back on the ground and try to drive.
My Gasser has the sprag case. Just moving the truck around on my place I sometimes have trouble getting 1st or reverse. If I am on dirt, I just put it in the gear that it goes into and drive in circles on the loose stuff. That is because I sometimes allow it to creep the wrong direction. Your case sounds like a lot more. That is why I suggested the TM recommended tire off the ground method.
Now, if you have an air shift, the shifter is going all the way and you still have nothing. Pull the transmission cover off the floor and pull the top plate of the transmission off. Look the shift forks and gears over for something obvious.