These are the only ones that make a difference
Nitrous plates, and no the throttle body spacers do not make a difference on these trucks due to the design of the manifold. These truck manifolds have huge plenums that snake around back to the same location for induction for the combustion chambers (which also makes them ideal candidates for nitrous due to the large space available for atomization). Certain engines will benefit from the spacer but they are generally a last mod or better spent on a cam or a custom tune. The ls6 manifold is a great upgrade for these trucks, as are the cam and heads if you don't plan on towing or adding some form of forced induction (lower lsa tends to save the low end torque in these lsx trucks).
The spacers are a cheap mod capable of producing small gains on certain engines but I generally convince my customers to buy another performance product or nothing at all so they can save their money for something worth purchasing.