Well a header might help, but more by taking the passenger side exhaust off of the #6 exhaust valve. The quest for power in a 3.0 is an elusive one. If you read around you will find that to get power from the 3.0 will take some serious investment and many folks will tell you not to waste your money and just do a 3.4 swap.
Intake and exhaust upgrades help, but I have read that one of the major issues with the 3.0 is in the head design and a lack of flow.
I am currently rebuilding a 3.0 to go into a 4runner with a blown motor. I am having the bottom end machined and I am having some larger valves installed in the heads. I have a line on some headers, used, that I am going to try and get. I figure that should give me a solid motor with ample power, I will makeup the rest with gears. By shopping around and doing most of the work, I figure I will end up with less than a grand in this little motor and it should be good for a couple hundred thousand more miles.
As far as where to buy a set of headers, look at LC engineering or thorely, but get ready to pay for them. I think a set from LC without the crossover pipe will set you back around $600.
To answer your main question, to get more seat of the pants power you need to match your gears to your tire size, for example if you have an auto trans and have added 33s, then you will want something like a 4.88 or even a 5.29 to give you the "pep" that you seek. Otherwise a good tune-up will do wonders, from there you just have to start reading and spend the money where you think it will do the most good for you.
Good luck,
Tucker