Duece, let's re-group on this problem a little bit.

First, can I assume that you have open differentials in both axles? If not, what type of traction aiding devices do you have in each axle? Some lockers and LSDs will give the sumptoms that you describe when they start going bad.

Second, what kind of transfer case do you have? Does it have a chain drive in it? If so, how long has it been since you had it apart and looked at the chain and sprokets?

Third, do you have a CV (double-cardan) joint on either of your driveshafts? Sometimes they can make a popping sound when they start going bad.