The 5.9 is basically the exact same engine as the 5.2...in fact, many of the parts are interchangeable. The 5.9 just has a couple more horses and a little better torque numbers. I love my 5.9, so much so that I went out and bought a chevy tracker to use as a daily driver so I can preserve/build my truck!
Anyways, I always say the same thing to someone looking at buying an already heavily modified vehicle...inspect the suspension components VERY carefully and make sure you know exactly what has been done to that thing. How many transmissions has it gone through? What shape are the ball joints/tie rods in? Are there any signs of obvious abuse from off roading? Something lifted that tall needs to be done right...if the previous owner cheaped out on anything or half assed some stuff, you're gonna be the one paying for it down the road