Well, I've read all the replies and find this all very interesting but I've got something to throw in here.

Having owned a Chevy 4x4 I was told by fellow 4x4 enthusiasts to NOT go with the biggest - free flowing intake and exhaust I could find. I had planned on a throttle-body spacer, K&N air filter and 3" exhaust. Apparently this was a no-no. This was because while it would increase horsepower, it would put the torque on the higher RPM range instead of the low RPM range, which is where all the slower "rock crawling" power is needed. Needless to say I didn't do anything, and have a nice - stock - Blazer 4x4 (which is for sale by the way... www.geocities.com/stevehurwitz)

With that in mind, one needs to apparently choose whether you want off-the-line power or top speed or something in between. If you want to smoke your tires you aparently don't want the most free flowing intake and exhaust, while for top speed you would.

Or do I have this completely wrong?