Truck advice

[Brian]

Question for truckers in the know.
I eventually need to get a bigger truck to pull a horse trailer. My wife's friend is putting hers up for sale because she can't get two kids (both in car seats) easily into the extended cab.
It's a 1999 Chevrolet Silverado 2500, Long bed, extended cab, V8/5.7L, 4x4 with all the bells, 72000 miles, 1yr old tires.
I'm a mechanical dufus and so I never buy used cars. But, they said they would gives us below blue book (14,000).
Are these good trucks? How long should this last? What are the relevant questions to ask, things to check when buying a used car?

Regards,
Brian