There is a thread not far from the front page here about the longevity of the V8 in these trucks. They are really great trouble free motors, close to the same MPG you would get with a V6 and tons of passing, mountain climbing power. That said, in 160,000 miles, if someone ignored your trans fluid or the diffs, you could have some nasty fluids floating around. Take it to the dealer and let them give you a list of what's wrong, they try to make money on service and will even tell you if the wipers need replacing. Make Sure LOW RANGE WORKS!!!!, can be an expensive repair if the actuator has failed from lack of use or water penetration. If it passes with flying colors, drives smooth, has good tires, shocks, seals, brakes, ect, I'd offer 7000.00 personally. If it needs tires or brakes or something big, look up trade in value and work up from there if it needs items fixed/replaced.
After reading about quite a few, not many but a few V6's with blown head gaskets, I'm a little weary of the V6's. There are soooo many on the road that are trouble free that it seems silly on my part but that V8 is a great motor and I have a small trailer that it would pull great.
Best of luck in your search/purchase, there are a lot of these trucks around. Don't get hung up on one, you might just have to travel a little further to find your "perfect" truck.
-jorge