Welcome aboard! How do you know the gears were changed to 4.56? It's very likely it has a Dana 30 / Dana 35 combo. It could have a Dana 44 rear end, but those are pretty uncommon.
It does look like a 4" lift to me, and I don't see any body lift either. The first thing I'd do is put some 32" or 33" tires on it. Those 31" tires look too small with the 4" lift.
This things are pretty darn reliable when properly maintained. There's a guy on here with 600k miles on his stock 4.0 engine. He's never done any internal engine work to it at all, only had to re-build the transmission a few times, and do basic maintenance!
Maintain it, and it will last forever!