hi all, i have a 1990 :ford: f250 xlt lariat 4x4 with a 7.3 ats turbo 5spd 372,000 km it runs smooth sometimes and then starts missing and when driving i can hear it popping out of the intake and my turbo boost gauge flutter as it pops. and when idleling it will somtimes smooths out for a bit then start running rough again. when i rev it up slowly it will somtimes fire on all 8 cyl i,am thinking it might be a sticky valve? or a broken valve spring? or could it be burnt valves?starts to miss bad on excelleration anybody have any thoughts on this? thanks.