04 gmc sierra 1500 5.3 died on me on the highway got it towed home starting going at it, hooked two different scanners to it and not throwing any codes (ecm is working bc the map was reading correctly but also the rpm was zero) anyways checked fire none checked injectors they wasnt working either(built fuel pressure then unplugged fuel relay then turned engine over and the pressure stayed the exact same) i assume it might be the crank sensor but i would think it would throw a code, anyways came back this morning and before doing anything for the hell of it i checked the gas cap and tightened it and it fired up perfect three different times and the last time i let it run and it died after bout 45 seconds (fuel pressure reads 55) and after it died its doing the same thing cranks but wont fire or start