I recently got hold of a 2004 1500 4X4 with the 4.7. The truck is mint for its mileage and year, so that's what tempted me enough to buy it even though the thing was knocking really bad. It was throwing a code stating a misfire. Replaced all plugs with new ( they looked like the originals ). With the engine running I disconnected the COP feed on each plug until there was no change in engine tone at that COP. Determined that #1 cylinder was dead. Switched COP with known good cylinder to dead cylinder, and visa versa, that had no effect on dead cylinder. So, determined that COP was good. Removed plug on dead cylinder, could see the plug was firing, ( looked used, light brown color ) so fair to say the injector was good. But, the cylinder was definitely dead and making the engine idle very rough with a really bad sounding knocking and LOUD tapping. So, off with the rocker cover. And there laying under the camshaft was a rocker arm!! So, I took the lash adjuster out, stripped it down ( it was seized solid ) cleaned it, got it working again, and stuck it back in the head. Removed all the plugs so I could spin the engine freely with a wrench, rotated the camshaft so the point on the lobe was away from the rocker arm, and reattached the arm. I was concerned that there may have been valve/head/piston damage so I rotated the engine by hand for the first few revolutions to feel for any issues, but it was all good. Everything back together, started it up. Rattled quiet a bit for the first minute or so, then quietened down once the oil filled the adjuster and it had warmed up fully. ( I did this outside in -15 c with the windchill - no garage ) Now idles smooth as silk - and this engine has 260,000km!! on it. Warmed it right up, let it idle for a good 30 mins. Did oil change, idle some more. It's now perfect. Not a knock or tap to be heard. Actually runs really sweet. So, I have a full set of new lash adjusters going in next weekend just to be safe. Regular oil changes are the key. Oh, and in all the videos I checked out on the net that had pretty much the EXACT SAME symptoms, a common potential cause given was timing chain/tensioners causing the misfire and sound. The chain in this engine definitely looks original but was/is working the way it should. So, I may have been lucky, but as this is pretty common on these engines if they don't get regular oil changes, it's a good bet that what starts out as sounding REALLY bloody expensive, could turn out to be a dropped rocker arm.

Peace.