starting problem..

[vgnope]

im having trouble firing up sometimes..ie; ill go in garage turn key and fires right up... 5 mins later or so turn key, cranking and cranking then it starts ,sometimes it doesnt.. ill eventually get th jumpers ,hook up and it starts right up..ill drive it and the volts are steady at 13.5/14..at a stop light,blinker on,the volts fluxuate.. its a 283 with hei good alt,batt,fuel is present, new cap-rotar,plugs wires.. is it the coil??ecm???this problem doesnt happen all the time, but it seems to be getting worse....frustrating...UGH