The 4.7L V8 produced (as advertised) 235 HP in the 1998-2002 models and 265HP in the 2003-2007 models. Same engine. Mostly. The major difference was the transmission. The first generation had the same A343F 4-speed that the 80 series had; the second generation had the A750F 5-speed. This change was not made to improve the output torque or horsepower - it was done to meet CAFE requirements.
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Note: the North American Land Cruiser/LX570 (2008-on) did not have the 2UZ-FE.
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I've driven (and owned) both, although not at altitude above 3,500-ft (that's the eastern continental divide - it's all we have here), and I couldn't see a difference offroad.