Toyota makes a great machine. You'll have the 3.4L V6 in that rig, solid engine if it's been cared for. Transmissions are solid in them, not any common problems at all with them. Things to check before buying would be to see if it had the timing belt and water pump replaced. If it's over 150K miles, they need replaced if it hasn't been. Parts can be a bit pricey for Toyotas nowadays, but if the vehicle seems like it was cared for nothing should break anytime soon.
** I have seen those engines blow head gaskets though.
**They don't get very good milage, but hey at least youd have 4wd to go about anywhere off the hard roads you want.
**Sleeping in the vehicle with 2 people and a dog is going to be TIGHT with gear to boot. If you're going to mostly tent camp or whatever outside, solid rig to travel in.
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@Jake Pemberton can give you a first hand expierence if he wants to chime in. He built a platform bed in the back of his for sleeping.