The 4.0L SOHC does indeed have problems with tensioners for its' timing chains (front & back). According to info I've read on these, it is important to replace the hydraulic tensioners every 100,000 miles or so (front & back). I've done mine years ago and could actually hear the difference... there was a lot less rattle at cold starts, for example.
The hydraulic tensioners are accessible from the outside of the engine and can be removed with a 27mm (I think?) long socket and a breaker bar. Be careful not to buy Taiwanese knock offs on eBay, only buy the original NOS Ford ones. I bought some cheap ones on eBay (Made in Taiwan) from a parts place in California and the front timing chain sounded like it was running loose - it made so much rattle I thought it was gonna come off! I had to put back the old tensioner, order the proper Ford-made part and swap it again. Only after putting the genuine part in there did it cure the rattle and restore quiet start ups. I tried contacting the eBay snake oil salesman to return the knock-off tensioners, but hit a brick wall (left them negative feedback as a result, for whatever good that would do). Lesson learned!
There apparently was an internal issue with tensioners also, where Ford in their infinite wisdom put plastic tensioner parts on the chain itself initially (then changed them to metal ones via a service bulletin or what not - wasn't a recall though, unfortunately). That is a lot harder to do and, for the rear one, requires removal of the engine from the truck. Hopefully all you need is to change the external hydraulic tensioners and you'll be good to go.
Good luck!
P.S. Also, I don't know about others' opinions, but I am a firm believer that a good quality fully synthetic motor oil does miracles for this engine and its' timing chains. For one, the hydraulic tensioners need motor oil (oil pressure) to work properly, so a good runny oil is best... especially in colder climates like ours out here (Canada)!
