I second the pinion bearings. Had that on my GMC and only made noise when giving it gas like yours.

 

Pinion bearings is going to be your culprit.Noise when accellerating is rear bearing being loade let off gas front bearing being loaded.I can tell you from experiencing same thing .Finnaly seal went out i went to change it took driveshaft off and pinion wiggling all over place .

 

I have a 99 4x4 that did the same thing, I thought it was the cv shaft, but about a week later the transfer case split apart while i was driving on the highway. I'm new to the 4x4 thing so its a definite learning process. My truck had the same problems right before the case went. hope this helps.