I rode around with 35 psi for a while. Ride wasn't bad. I think some have done 42 psi, but that was with a heavy load in the truck. The problem with going with more pressure, is less contact with the road and so less traction. Plus the center of your tires wear out faster and the ride is not as smooth. You can go up in pressure, just make sure your tire "footprint" has enough contact with the road to be safe and don't exceed the warnings on the tire for max psi.

I ran recommended pressures (30 front, 33 rear) with mine early on until I started towing quite a bit (was concerned about the tires looking very low), and have now bumped it up to 32 front, 35 rear. I like the balance between a decent ride and enough pressure to tow without squishy looking tires. This may be due to my having the 20 inchers.

Parker TireSaver Nitrogen Tire Inflation Filling Systems

This web site might lead you to some good information. Nitrogen is the new magic with the tires, NASCAR uses it. Semi drivers also. I don't pretend to be an expert but my Toyota Tundra came with bridgestone tires, which I immediately traded for Michelin LTX AT2's. these are the same type of tires we use on our ambulances. I buy my tires at the Tire Barn, these guys are awesome and they put me onto the nitrogen. Actually they filled the tires on our travel trailer for a trip out west of over 8,000 miles. The tire pressure never deviated. Also, I noted that when I was getting my tires filled, I can't tell you how many Harleys came in to have nitrogen put in their tires. This worked for me. I am equally picky.

Nitrogen is good stuff. The pressure doesn't change much with the ambient temperature and it is less likely to leak out. I know a lot of guy who use air bags on their trucks and most keep Nitrogen tanks in their trucks to run in the bags.

The obvious next question is where does one go to get Nitrogen? --After going to the above link and searching for a place to get N, I found Lufkin TX, my hometown where I visited over Christmas has it - of all places, we're talking 35K pop. An and independent tire place to boot, go figure.

I've got OEM 20" alloys and use 30 front 32 rear per door jamb specs; however, I don't haul anything - except azz of course.

RarJar, you especially may be interested in this explanation of N, especially since it comes from Cook Tires in Lufkin. You may want to check them out.

Excellent info about N in tires:
http://cooktire.com/nitrogentireinflation.html

You might call around to the local shops and see if they carry it. Some fill straight from nitrogen bottles and might not be listed on that site.

I have the BFG Ragged trails on mine and I drove it a few days at the recommended tire pressure on the door. The Tundra drove terrible with the low pressure. I drive on very curvy 2 lane roads and the truck plowed though the corners and constantly set off the VSC chime. In addition I was wearing the outside of the tires in a big way.
I now have 40psi(44PSI max rating), and the trucks corners much better and the chime no longer goes off. I guess that more pressure stiffens up the sidewalls a little.
I should also say that I usually have a trailer of some sort hooked up and or 500 or more lbs. in the bed.
The ride is a little harsher, but is way better than my solid axle vehicles.
I have 9k on the truck now and the tires are about 60% gone, but the wear is even.
This is the 4th truck that I have had Ragged trails as original equipment(2 Tundras and 2 Titans), and the most I ever got was 15k miles out of them. Either the tread was worn down to nothing, or I had so many sidewall flats that they couldn't be repaired.

Sky, you have the 18's, right? I am wondering if maybe I should step my 20's up a tad on pressure. I am running 2 psi over on both front and back from the recommended 30 front and 33 rear.

Yep, I have the 18"'s. I would go ahead and experiment with the pressure. It has always been my opinion that the factory recommended pressure is always to low for my situation. I think that the factory pressure may give you a softer ride, but you sacrifice cornering and comfort/safety as far carrying a load or towing.
To me, a p-rated tire is a bad choice for a working truck. I will be getting some BFG AT's, I love their thick sidewalls and the fact that I can run them at 45-50lbs of pressure and have little if any sidewall bulging with a load or towing.I also like that I can air down to 20lbs or lower in soft stuff and have the protection of the thicker sidewalls.
I also don't like the low sidewalls we have on the 18' and 20's, but there isn't much we can do about that if we want to stay with the stock sizes. I don't want a taller tire as I like to keep the gear ratio where it is.