Something like the ones made by airaid work well but only with the addition of a mass airflow filter such as k&n. Alot of the guys I know use the filter and spacer combination provided by airaid. Otherwise I dunno. http://www.airaid.com
I have one, it seems to shift your powerband up...they say they give you better lower torque, but i don't know. i made my own using the gasket that goes on the botm of the TBI as a template, made out of 1" alum. i think it helped give a couple of extra hp at about 3000 RPM...
you are just backwords Fishy. A throttle body spacer makes more upper end HP. It is the samething as a carb spacer. It won't hurt to put it on low end wise, but ti doesn't do much to the low end either. I haven't noticed a bit of change on my truck. I have had it on for a fewmonths.
This is a familiar thread (actually, I think I've asked about these myself). The one answer that stuck was that 1996 and newer vortek engines would not benefit from a spacer. The intake was modified in 96 which pumped the vortek from 165 to 195 HP. I will spend my money on something else....probably beer.