Check the filter, float, accelerator pump and fuel pump in that order. Also check your gas level, your gage may be off too.
I am pretty sure this is not the problem, but a dented gas tank can be the culprit too. Sometimes a dented gas tank can move the gas away from the fuel line causing the engine to starve when climbing hills. But in your case you said that the truck has been running great until yesterday.
Wouldn't hurt to check your wires either. Once in a while a loose wire on the ignition or coil will give the same effect when climbing a hill. It feels like it is starving or chugging.
