My 99 ranger 4wd 3.0 has 190k miles on it with no engine difficulties at all, other than the poor mileage it has had since brand new. I have kept up with basic maintenance and have replaced the ignition wires once. This truck has been used as a work truck and often carries and/or tows heavy loads of firewood. Spends a lot of time in 4wd carrying loads also. My only suggestion is to avoid those multi-electrode spark plugs, they don't seem to stand up to heavy load situations very well. No oil burning at all and I have only dropped about 1 mpg over it's life so far.
I also have a 99 taurus and a 99 sable both with the 3.0 vulcan engine. The taurus has 280k and the sable 210k. Again, neither has had any engine work except basic maintenance. The taurus is finally burning some oil, but only about 1/2 quart at oil change time.
Like others have mentioned, even if your motor pooches early, if the price of the truck is right, 3.0 engines are a dime a dozen used.