Chrysler has never really said much about the design of the hydraulic roller lifters used in the 5.7 Hemi.
Apparently some Chrysler engineers told David Vizard (see link below) that they had tested these lifters for 'anti-pump-up' at rpms up to 6200 rpm. A normal hyd lifter won't go that high without mods, so the Hemi lifters must have some internal mods.
If Chrysler made their Hemi lifters 'Rhoads Style' with internal bleed down, that would also potentially explain how an engine with a torque max at 4200 could still produce 330 ft-lbs at 2000 rpm and 300 ft-lbs at a (hard to believe) 1200 rpm.
See how the torque curve 'flips upward' in the 1200-1600 rpm range. That is odd, and might be due to lifter bleed off that is designed in to the lifters.
If the Hemi lifters are 'bleed down' designs, and if the quality control at their manufacturer is not superb - or if new truck customers are 'ruining' the hydraulic lifters by running them to 6400+ rpm on engines that have only a few miles on them - then it might be a 'root cause' of the Hemi tick.
If the Hyd Lifters collapse too much,
you would expect slack in the valvetrain.
Slack in the valvetrain would lead to
broken valve springs,
bad valve seats, etc
Other posts in forums have talked about the manual's call for 5W-20 oil in the 5.7 Hemi. A low viscosity, high film strength oil is a sign that someone is trying to deal with a 'tricky' hydraulic lifter requirement for lubrication. The narrow range of 5 to 20 is another sign that 'controlled leakage bleed off' must lie within a close range to something to work properly.
Chrysler has messed up on hydraulic lifters before, their first roller lifters in the late 1980's pre-Magnum 'roller' 318 had chrome plating that flaked off and the staking on the roller axle ends was not consistent.
What are the 'real world' implications of this?
1. Try to buy a Hemi with almost no miles on the odometer - then break it in gently yourself for the first 3000 miles with several oil changes to flush out small particles. No need to change the filter, just change the oil, perhaps every 500 miles. Don't used old fashioned ideas about how to break in an engine that was only valid back in the days of flat tappet lifters. Consider custom ordering a truck and tell the dealer you expect single digit mileage on the odometer when it arrives.
2. Pay close attention to the oil you use. Watch your oil pressures closely.
3. If problems develop in the valve train, always insist the hydraulic roller lifters be replaced too, no matter what BS the dealership throws at you.
4. Insist that all 8 cylinders valvetrain be brought up to new, not just the one failed cylinder.
5. Learn about Small Claims Court rules for your State. DaimlerChrysler is afraid of Small Claims Court because they almost always lose against a well prepared customer. Print out the Popular Hot Rodding article and be prepared to explain to the judge how this small part caused these high $ repairs and lost resale values. Know your state's Lemon Law too.
6. Don't even be the least bit bashfull about insisting that DC make your Hemi right and re-imburse you for expenses. DC top brass have admitted to Wall Street bigwigs that the 5.7 Hemi has been the 'Profit Machine' that has made them oodles of money. It costs DC less money to make a 5.7 Hemi than a 4.7V8 but they charge a $800 premium! The German honchos at DaimlerChrysler reached back into the American engineered Hemi 426 past glory days and pulled their chestnuts out of today's fire. Have they sent the old retired Chrysler engineers (like those profiled in this month's Hot Rod Magazine) any bonus checks to go with their pensions? I bet not.