As a starting point, check out the tyre placard which should be located on the drivers door frame, near the locking mechanism. It should be visible when you open the door.
Stock wheels?? What's size is the rubber? Etc? If that are stock the previously mentioned placard will be perfect for advice, if not let us know and we can suggest a pressure.
On a standard tyre size I run around 33-35 psi but the last time I went away and towed I went up to 45 psi. The fuel economy and ability to keep up momentum up hills was vastly improved and the ride wasn't to bad with the extra weight on the back but with no load it's a bit harsh so I will drop them back to 35 psi and see how it goes.
I run 34 Rear & 36 Front in 32" Bighorns for everyday driving 25-30 once on dirt/ gravel. Then lower to suit conditions - mud/sand etc. If you are running the standards treads I would probably be going 36-38 depending on load in the rear.
Some people run with the 4PSI rule on the road where you can set your cold tyre pressures and aim for max increase of 3-4psi after about 15mins of driving. The problem with this is there are way to many factors that play a part such as ambient temp, sun, surface type, surface temp, load on tyres & the list goes on...... Just my opinion but someone may correct me that this method is proven.
In saying that I used it to help set my pressures
It comes down to trial and error for your setup.
I dont know why al these tyre fitters try and insist on 40psi!! its just to much in an empty ute.
I found in any of my utes if i run more then 32-36psi they start to wear the centre of the tyre out on the rear, this is a definite sign of over inflation.
i personally run 32-34 in the rear (empty) and 34-36 in the front and find that my tyre wear is spot on, however i do ALLOT of freeway driving and at 120kph the rotational force tends to balloon the tyre more then normal so the centre wear will be more noticeable at those higher pressures.