I've been looking into mods to increase performance of my 2000 4.0L. I live at 6000 ft. I've looked at all the usual intake and exhaust mods. Here is the deal. I've seen articles on the new 4.0 HO changes. They basically say than the improvements made to the newer HO intake/exhaust are good. I can bolt stuff on, but won't see as much improvement as older engines. Meaning less improvement for my dollar spent. I can't find any hard numbers for newer engines. Also at 6000 ft., I loose 20% air/power. So to me that is the same as saying my intake/exhaust moves 20% less air mass, so it's not as restrictive. Does that make sense? Am I going to see any real improvement modifying my intake/exhaust or is it all just snake oil? Can I make any real imrovements short of supercharging? The point being is that I have less air to move to start with at altittude. When I wheel it's usually up to 10,000 ft. Any input is appriciated. Thanks