Here is a bit of information on the '19 6.7s. The HO gets less compression to compensate for more turbo boost as well as different software.
Revisions to the Cummins 6.7-liter inline-six turbo-diesel are significant. Ram claims the new engine is 60 pounds lighter than its predecessor. New pistons, said to be lighter and stronger, utilize low friction rings and ride on new forged connecting rods in a new block made from compacted graphite iron. The new cast-iron cylinder head is home to new rocker arms, exhaust valves, and springs. Compression ratio for the standard output is 19.0:1; the high-output version uses a lower 16.2:1 ratio to facilitate additional boost. Speaking of which, the improved variable-geometry turbo mounts to a new exhaust manifold and is capable of delivering up to 33.0 psi of boost; the intercooler has been enlarged to the point where Ram calls it the largest ever fitted to its diesel pickups. The redesigned fuel-delivery system features a new pump running at 29,000 psi. The standard-duty model is rated at 370 horsepower at 2800 rpm and 850 lb-ft at 1700 rpm; the high-output version clocks in at 400 horsepower and 1000 lb-ft at 1800 rpm.