just replaced my motor in my 1998 3.0 v6 ford ranger with a used 3.0 v6 from a action auto that tested the motor before the sold it to me it ran and had 165lbs of compression in each cylinder i just got it in and got it running it fired right up but it sounds like its missing and doesn't have much take off power and back fires around 55 mph i pugged a code reader in and it read that the number 4 cylinder has a misfire i changed the plug wire and sparkplug and still didn't help i also have a red vacuum line open that that runs under the distributor that was sucking air so i plugged it and it still didn't help

 

Shouldn't have a distributor .................

Your firing order is wrong, do it myself all the time on 4.0l
Coil pack
1 2 3 << easy one
5 6 4 << odd man out, lol

Or same thing
4 6 5
3 2 1

These are "matched" cylinders, 1 and 5, 2 and 6, 3 and 4
Each of these sets is at TDC(top dead center) at the same time, one at end of compression stroke one at end of exhaust stroke, Fords "Waste Spark" system fires both spark plugs at the same time, spark on exhaust stroke is "wasted", so there only needs to be 3 coils in the pack.

Also double check the wire itself is going to the correct spark plug/cylinder

 

i know it doesn't have distributor i just dont know what its called haha but ya i did check and i made sure the wires are in the right place