The valve issue that Steve brought up is one you are unlikely to encounter. This was not a problem with durability , but simply that some valves were not angle cut prior to be shipped for install in the motors. This resulted in a slight drop in horsepower. There were only about 200+ cars involved and what many were unaware of was that quite a few were caught at the Plant and fixed. If memory serves me right , this was on a few cars built in the Jan-March 2003 time frame. It would be surprising to find one out there that was not repaired, as Dealers were sent notices on the specific cars in their inventories.
I assume you are actually also thinking about 2006 , which was the last year of the 510 hp ( SAE corrected ) 8.3 liter motor, and overall there were fewer problems on the Gen IIIs than were encountered on the Gen IIs ------- an overall very few issues compared to other model vehicles ( i.e. Corvettes ).