depending on how early that motor was built it technically coulda been built when Mercedes owned dodge. the 4.7 came from their 4.5. only a few tweaks for the truck market. problem is they used the Mercedes head design with valve seats that are fitted to the heads not machined into them. which means when they get hot they can unseat, warp, fracture, drop out. Mercedes engines absolutely hate hate HATE heat. and since the top of the cylinders are the hottest part of the engine even a little overheat shown on the gauges is a huge heatup on the heads. my vote if the engine isn't shot to hell. the heads are fried, try testing for compression loss on each cylinder, look for cracks, check out your spark plugs for signs of scorching effects on the ceramic.