theres a vibration on 2001 Dodge Ram 1500

between 40mph and 55mph there's a vibration like a wheel is out of balance when the o/d is on but goes away when o/d is turned off what would cause this

Asked by for the 2001 Dodge Ram 1500
Check engine light on or flashing? Vibration or a fast jerking like a misfire? Misfire more likely to show up in OD than other gears, more load on engine/ignition system.
there's a misfire on #1 and #8,changed the cap and rotor[yesterday] and put new plugs and wires on about 6 months ago but still have misfire on #8.could bad cap cause wire or plug to go bad?
Wires crossed? V8? Cause firing order is 1-8-4-3-6-5-7-2. 1&8 can easily be crossed. Try swaping wires between 7&8 to see if misfire follows wire. 7 is rear plug on left, 8 is rear plug on right. If misfire does change with wire replace wires, if not then check plug, compression and injector pulse or have this checked!
put new wires and plugs in but the vibration is still there between 40mph also when I gas on it the check engine light blinks but goes's a 2001 5.2/318 v8 with 100250 miles next thing is a compression test.what should the compression be?
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bad vibration between 40 - 50 but if i take off fast like paddle to the floor no vibration 1997 dodge ram 1500
Had the same problem in my 2001 ram 1500.Found that new plugs,cap rotor,and wires took care of the problem and its been running fine now for about 2 years.A misfire caused the problem