I get a vibration at 3800 to 4100 rpms . Doesn't matter what speed or gear ,towing or not just in that rpm range . I've changed the transmission mount, motor mounts, had drive shafts balanced , new u joints had center bearing changed . transmission fluid changed with lube guard added , and filter changed , torque converter drained also. The truck runs fine shifts fine no shudder, bumps, hiccups, HHHHEEEEEELLLLLLPPPPPPP............

 

Well, if it happens at a specific rpm range, you wasted your money chasing drive train repairs. Then you say "not just at that rpm range". Please explain further.

 

The only thing you forgot to do is give us your truck details.............

 

!994 f 150 xlt extended cab 5.0 automatic , to answer the other comment it vibrates whether I'm towing my camper or not. It only has this vibration in that rpm range sorry for any confusion.....

 

It has to be engine related. Possibly a beat up harmonic balancer.

 

Harmonic balancer is next on the list to change ,fingers crossed..........

 

Pull the drive belt and rev it up - if it still vibrates that's most likely what it is. If the vibes stop it's one of the belt driven components.

 

Either rerouting the plug wires per the label on the header panel or the harmonic balancer fixed this mess. woot woot what a great day yeah me.....Never new plug wires to have a set diagram for routing learn something everyday