Easiest way to find out is to put the trans in neutral, the t-case in 4wd and lock the hubs, push your truck on a flat level surface don't try and drive it. If it becomes progressively harder to push and then becomes completely impossible to push the gearing is different in the axles.  Do not try to drive it this way it will not be pretty, offroad it could scrub the tires so that it may not hurt it but engaging it on pavement will lead to the total distruction of the t-case. Now comes the next step finding out what gearing you have.