318 T.B.I.I've had this truck for 5 years, When i got it it idled rough but ran good,still dose.The checkengine lite was on when i got it had a broken vacume hose on the map sensor replaced lite has never came on again.It idles like it's on 7 clyinders but soon as you increase the rpms it runs good, It also as of late has a small bog sometimes not bad .Here's what i've done so far new timing set,tune-up I.S.C,fuelpump an fuelfilter.coil, checked all vacume hoeses , Has 150 compression on cylinders, idles @ 14 inches vacume, no cats true duals i had installed,Sorry so long just tired of the rough idle

 

is there sort of a miss but it changes where it is? if so you may have a distributor problem. the hall effect may be bouncing off the pickup.