have A 2003 1500 HD silverado 4x4. with about 135 thousand miles on it, it starts but takes a few starts to get it running. i have had the starter, alternator and battery tested all are good. before I start ripping wires and fuses and what not anyone have an idea where to start. she normally starts on the 2nd crank but with cold air approaching I wanna get this fixed

 

Are you saying it fires up then dies or does it sometimes crank over several times before firing and running?