Fuel Pump Or Fuel Injectors

my question is how do you determine that your fuel pump is going out.  Yesterday I was lazy and didnt get gas, on my way to the station I had to sit on a hill. when I hit the acceleratior the truck was very hesitant. I put the gas in and started on my way.  The engine light started blinking and the truck one again was hesitant.  I put fuel cleaner in the gas tank and drove around for about ten min.  Went and got theoil changed (it was due for one) disconected the battery to reset the computer and at first the light was off but as i started to go up another hill the light came back on blinking. I have noticed this morning that it only becomes hesitant or the light blinks when im going up hill. Can anyone tell me is this a possible injector or fuel injector problem I may have mad worse by allowing it to run so low on gas.