Have had three different mechanics tell me my timing chain is loose and on way out. Truck has a real hard buck sometimes, but not always. I can hear what sounds like a loose chain. 03 5.4 with 138k miles. I can do the chain for 1100.00 to 1400.00. Advice needed. Pretty broke right now so keep that in mind.

 

Aside from the labor, gaskets and any parts, here is what's behind the chain cover.
The chains are tensioned by oil pressure acting on small pistons to put tension on the chains.
It may be that the tensioners are just worn allowing the chains to hit the case. Of course the camshaft timing will change a bit as will the fuel injection timing and ignition timing when the chains are not in precision control as detected by the Cam sensor on the front of the drivers side head.
You need to evaluate the situation after it comes apart.
If the motor was run over the long term with heavier oil than reccomended, it may be the reason the tensioners wore so soon from excessive pressure against the chains.
My 4.6 is at 152,000 miles and runs as new with no noises of any sort.
Always had 5-20 Motorcraft blend oil.
Good luck.

 

Jirwin, Does your truck buck around 50-60mph in Overdrive at 1200ish rpms?

 

It is never a set speed. It has happened at that speed in overdrive though