I think my 05 probably has the same injectors as your 03. I was told years ago that the lift pump would fail that supplies fuel to to injector pump and it would still run. After continued use with a failed lift pump, the injector pump or injectors would fail. Two of my injectors went weak at about 125,000 so I replaced them all and put in a external pressure pump system with filters and it worked great every since. The only starting problem I’ve every had is when my starter went bad. I replaced it with an O’riellys unit that worked up until it started getting slower to turn over the motor. I replaced it and now it starts like new. Two revolutions and she fires right up.