my trucks bin acting up alot latly.. when i start it up she revs kinda slow... and when driving below 2000 rpm it just crawls.. then starts to pick up a bit after 3000.. but nothin like it should be.. then when i shut the truck off.. she turns over alot!! before it fires.. then once its running.. i try to turn the idle up.. it revs at 1000rpm then drops down to 500 rpm.. then after sitting at the light it'll die before it goes green. so i gota keep reving.. i tried setting the timing today.. i retarded it.. advanced it.. nothin still doing the same thing.. so im thinkin maybe the distributer gear is worn?? or a plug isnt firing?? no idea wut it could be.. maybe a vacum leak?? i put my gauge on and it read 12 i think.. with my 280 magnum cam.. but this was also low rpms cuz the motor won't idle very well right now.. any have any ideas or bin in this situation?? thanx alot for any help.