Towing power mods?

I recently bought a ~5000 lb travel trailer to drag around with my '05 Taco on occasion and would like a little extra power. I've got the 4.0 V6 and auto trans. It's a TRD Double Cab if that matters.

I've got the weight distributing hitch and the trailer brake controller so I should be covered there. My truck came with the towing package stock, so I believe I should have a decent tranny cooler already. Do I need more? Do I need a gauge so I can keep an eye on tranny temps, or should it be fine as long as I drive reasonably? How about the rearend? Any heat issues in the rear diff while towing heavy loads long distances?

I'm not looking to be able to go 90 everywhere...I usually stick to 65-70 while towing, but I live in Utah and frequently drag the trailer several hundred miles, much of it above 6000 ft in elevation. 500-1000 miles will be pretty standard if I take it out for a weekend, much of it on 2 lane highways in the mountains.

I'd like more all around power. I've read on here that the aftermarket CAI's don't really do anything except make more noise and maybe help a bit above 3500 RPM's. A lot of people are really high on the AFE Pro Dry drop in filters, but I can't tell if that's because it's just easier and less expensive, or if the results are the same? If the CAI's do help with power, which one is preferred? AFE? K&N? Someone else?

What other mods will help? I know modern exhausts are pretty good...do any of the cat back systems and such help with power? Or are they purely a sound mod? I'm not anti-sound, but a badass rumble from the exhaust doesn't impress the 11 feet of wall that is the front of my trailer. An extra 15 horsepower to go with the rumble on the other hand...now that's worth looking into.

Any other mods to consider for extra power? The truck has more than enough power for my everyday driving needs, but another 10-25 horsepower could come in handy when towing in the mountains.

 

Well Doug thorley long tube headers are a gain in power, but if you really want more power I vote supercharger

 

if you're not looking to install a charger look at some exhaust and intake then get one of these http://www.urdusa.com/product_info.php?cPath=66_72&products_id=1260518754
gadget at urd will be willing to help with your tune.
oh fyi doug thorley long tube will lose you some low end.

 

Check out the thread "6 Cylinder Towing Review" in the Towing forum.