Well, first how much is the person asking? If it's missing seats and the leather is crappy, that souns like a pain. Unless you find one cheap at a junkyard, those bench seats are not that cheap to replace as far as I know... especially with leather upholstery.
Mechanical inspection: before driving, pop the hood and check out the engine compartment. Look for any slicks of fluid stains (oils, coolant, whatever). Look around the seam of the intake manifold and around the thermostat housing. Sometimes these truck leak coolant form there. Check the seams around cylinder heads/valve covers. Make sure the gaskets aren't popped out and there are no signs of fluid leakage.
When looking under the car, first look at the pavement under the car real quick for any stains/puddles. Look under the engine/oild pan for any moisture or fluid drips. Check the back of the oil pan/front of the transmission. That is the rear main seal and higher mileage trucks like these sometimes end up leaking oild from that. if it was leaking from the rear main seal, you'd probably see a fairly obvious spread of moisture/fluid all on the back of the oil pan coming from above it. while you are under there, check out the condition of the fram and exhaust. Look for bad rust and any rusty spots, holes, or any sign of breakage in the exhaust system. You also generally want to look for any kind of fluid leaks. Vehicles should be tight as a drum as far as fluid is concerned. Nothing should leak (in a perfect world). At all. Check the brake lines, differential(s), axles. Try and use your best judgement. It should be pretty obvious what is just water/mud and what is actual oil, lubricant, or brake fluid or something.
Driving: When you go to drive it, before you move at all, keep it in park and press down the gas pedal a few times and check the brake pressure. Good brake pressure will make for a stiff pedal pretty early on. It should get stiff without pressing it too far to the floor. If the pedal feels kinda soft and has a considerable amount of travel, then the brake pressure is not that great. While still in park, push down the gas a bit and tach it up; check the smoothness of the engine. With no load on the engine, it SHOULD rev up very freely with no hesitation or stuttering. Now, with your foot on the break, put it into reverse, Neutral, Drive, 3, 2, 1, and then back the other way back to park; one at a time making sure the transmission engages the gears. I would suggest (if the car is not back up against a wall or something) to put it in reverse first and make sure reverse works fine. Either way, when you go to drive it, just pay attention to the tachometer and the sound of the engine when you are in drive. Make sure the transmission shifts smoothly and at a low RPM (this would be when you are driving smooth and calmly). When driving with gradual acceleration, these transmissions gear up at a low RPM. If you get to go on the highway, see how the acceleration is and mash it going on the on ramp. Going from like 30-40 mph steady speed to wide open throttle should make you trans downshift with considerable force, and it should get up to speed pretty quickly.
This is all assuming everything in the vehicle is basically stock. Hope I helped. I wish I knew last year what I know now, back when I was car shopping.
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