when it will not start does it physically crank over ?
when you are cranking it when it will not start is the theft/security light on or blinking ?
ok the problem is going to be the ignition switch
the passlock sensor that reads the key is built into the ignition switch
if one key worked and another key didn't work we would have a key issue but since no matter what key you use this will act up replacing the ignition lock switch will correct this problem
this is a very common problem for these trucks # XXXXX is the ignition switch