When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
A quick search would have found the answer faster...
The fill and drain plugs are on the rear of the transfer case. If you can't see them when you crawl under the truck, that means your truck has a counterbalance weight on the rear of the transfer case. Simply unbolt the counterweight (4 bolts) to gain access to the plugs.