Grab a beer, relax and read
First and foremost, the V8 and the transmission attached to it are as close to bullet proof as Ford has ever created. The AWD system, when maintained properly, is great for on-road use. The truck is awesome in the snow with good tires on it.
Be aware that when it comes time for tires, you will have to buy 5. One each corner and the spare. You have to rotate all the tires frequently on the AWD system as a slight difference in the circumference of them can contribute to problems with the transfercase. (I suggest rotating tires at every oil change)
A nice little checklist of things to check on the AWD
Front sway bar links (easy 30 buck fix) connects front swaybar to the lower control arm, these tend to break frequently
Torn CV axle boots Turn wheels either direction, look at the rubber boots on the front axles
Front driveshaft (lay on your back, grab it and shake. Should very little to no movement in any direction. Not a cheap fix, close to 300 for the driveshaft, if the problem is in the diff you will spend much more $$)
Rear driveshaft (same checks, can replace U-joints @ about $30 each)
Crawl under it looking for leaks at the spots where the
transfercase/tranmission connect and at the output shafts
Look for leaking pinion seals on front and rear differentials (leak where the driveshaft connects to the differential)
Run your hand across the tread surface of all 4 tires, feel for cupped or un-even wear, beware of brand new tires, they could have bought them to mask other serious problems.
Take it for a drive, listen to what the truck tells you. Humming, grinding, popping, snapping noises should be non-existant. It should drive straight and true with no vibrations. Go over varying sized bumps, listen for creaking/groaning/thump or clunks.
It should brake straight and true, no vibrations or pulling to either side. Try the E-brake, listen for grinding.
Try every option available, the electric seats, tilt wheel, lumbar support, Smoothness of the shifter, OD shuts off, when you start it it fires right up. Turn the wheels all the way to one direction and drive it slowly in a circle, it should not hop or make any noises. If it hops it could be a transfercase issue, ($$) popping/snapping noises are most likely the CV's.
Try all the electric windows, electric locks and electric mirrors. Manually lock each door and try to unlock it with the keyfob and manually.
Try to open the rear doors from inside the truck.
Look for evidence of rot under/behind those pretty running boards (Very common spot)
Look for rot around the rear wheel wells, the "dogleg" at the rear door, and all 4 door sills.
Check the rear hatch for rot along the bottom edge of the hatch door inside and out side the truck, also the hatch cylinders should hold the hatch up unassisted
Open the hood, the hood cylinders should hold it up. Check the back side of the radiator, area around the waterpump for evidence of leaks, look at the gooseneck where the thermostat is for leaks, check power steering lines for evidence of leaks, open the air cleaner (this will only let you know if they are being truthful about always taking care of it), look at the valve covers for leaking around them, with the engine running listen to the alternator for weird sounding bearings, rocker arm "ticking" or what can be described as ",marbles in a tin can" sound. (that can be a host of things, all rather expensive to fix)
When you have the front wheel turned in one direction, you can lift the flimsy black "skirt" in the wheel well to get a look at the side of the block and what the wires look like. Take a sparkplug wire off and look at the spark plug, how old does it appear to be? If you can, take out a sparkplug and just check the condition of it.
Look under the seats, in the back under the mat, look everywhere for evidence that the truck was a travelling trash-bin that was just recently cleaned up to look cherry. (behind the rear seats, theres a spring loaded "trap door" that if you fold it towards the rear, you will see all kinds of things if it was a trash bin)
Look up on the headliner, some owners have reported a small leak around the sunroof, it will stain the headliner a little brown and may cause the fabric to peel away from the backing.
Check the function of the rear view mirror, (if it has a slide switch on the lower front of it) it is supposed to control turning the headlights on automatically, the length of time the headlights stay on once you exit the truck and also be "self dimming" (IE: no night time setting)
Checking all of those will give you a good handle on the condition of the truck.
Good Luck
