The 4.7L High Output was introduced in 2002 as standard equipment on Overland models, special order on Limited models. It was not available on Laredo models, but some of the 2004 Rocky Mountain and Freedom edition models had the 4.7HO as a special order option.
The V8 High Output adds a ton of upgraded hard parts to the standard v8, bumps the compression ratio up to 9.7:1, adds a forged crank, and makes an extra 30hp/30ft-lbs of torque. The nice thing is that it makes the extra torque EVERYWHERE in the power band, not just up high. You'll be able to feel a difference right off of idle.
In addition to the forged crank, the pistons, rods, bearings, heads, valves, intake manifold, fuel injectors, airbox, air plenum, intake tube, and spark plugs were also changed. The ECU was also modified and the engine is equipped with 2 knock sensors to allow peak performance with higher octane fuel.
As for maintenance, the HO is no worse than the standard v8 and only has a few unique maintenance items: spark plugs, air filter, oil. The rest of the different parts are not maintenance items and should never fail in normal usage.