I've got a 01 silverado with an 8.1L that the problem origionally started as a random Crank with no start. It would be totally random too. You could drive it all day then shut it off and it wouldn't start 5 min later. but then 20 min later it will start no problem. does it cold or hot. fuel pressure requlator is good. NOW i started it up this morning and it is runing really rough!!! Check engine light is flashing. Checked the code and it is PO300. Miss fire detected was on cylinders 5 and 6. More on 6 then 5 but 6 is constant misfire and 5 will stop misfiring above about 2 thousand rpms. Any ideas?