This 2003 UL seems like a good deal from Arrowhead Lexus
https://www.arrowheadlexus.com/auto/...a-az/86913295/

 

No they are not. The power is the same in ALL year models. In 2006 the US government changed how they measured Power, Torque, and Mpg.
The LS430 engine has always been 207kW = 278Bhp = 282hp(new US, also German PS or PferdeStärke) = 290hp(old US).

Why 278Bhp? Because at the time the LS430 engine was developed the Japanese car manufacturers had a voluntary agreement via (1988 to 2004) via JAMA to limit all engines to no more than 280Bhp as it was thought higher power would cause more accidents/fatalities.
In 2004 this was dropped when they realised that power has very little effect on accident/fatality statistics. That is why Lexus went from the 278Bhp 2006 LS430 to the 380Bhp 2007 LS460.