I would say if you've made sure you're AC system is operating correctly then you probably want to look at helping your truck run cooler.
One thing to think about are hood louvers, they're used by US Border Patrol and help lower the engine bay temps:
http://www.hoodlouvers.com/products.html
If that's a little too extreme or you want an OEM look you may want to look at the Escalade vents on the side and make them functional.
Also if your truck is not equipped with the heavy duty trailer package, then you may want to think about adding an engine oil cooler and a transmission oil cooler.
Also look at window tint on all windows including windshield and sunroof. If laws are strict there or dark windows aren't your thing, they make film that blocks the heat like tint but is completely clear.
http://tnttinting.com/node/1228
So if your AC system is functioning correctly then 131f may just be too hot for it to keep up and you need to get the engine bay's temps down.
Are you just using your truck for short trips to get from A to B or are you working out of it?
And I've always experienced ice ice cold AC from Fords. My '96 Taurus and my buddy's '00 Ranger would make your teeth chatter. Granted that was when the vehicle was actually running!!