If you're talking about true overlanding -- dirt roads, fire trails, across the desert, up the continental divide and down the occasional interstate -- consider a 70's era full-size jeep Cherokee or Wagoneer. They have a decent amount of room inside for equipage and supplies. Put the rear seat down (or eliminate it altogether) and you can sleep inside. And, because these things came from the age of steel, they have an honest-to-god frame like a real truck, not a uni-body.
They're pretty rugged, with Dana 44s front and rear, the famously durable TH400 transmission, inline-6 or small or large v-8 engines, and QuadraTrac full-time 4wd.
The QuadraTrac (Borg-Warner 1339 transfer case) has a limited-slip center diff, and is arguably one of the best full-time 4wd systems for loose-surface driving. (Ask Rich Severson about how he managed winning seasons driving these things 5 years running!) Just needs occasional fluid and cleaning. Chain replacement can be performed with the case on the vehicle.
Now, if your definition of 'overland' is steep-rock crawling from one mud-bog to the next, there might be better choices.