With the 2004. 5 model year a new swirl configuration was implented for the cylinder head as part of the combustion recipe change. So techically 2003 and early 2004 cylinder head castings are not the same as 2004. 5 and later. But for the way TCluff's truck is configured, it may not make that much of a difference. Swirl is changed by changing how the intake runners of the cylinder casting are configured.
Also, in 2004. 5 the inconel exhaust valve was introduced. But, like jwilliams3 stated, a new exhaust valve was introduced for 2006. This is NOT the same exhaust valve as pre-2004. 5 model years, it is an all new material, hence the reason for the increased valve lash.