Tractor motors, whether gas or diesel, are designed for their best fuel efficiency at 540 PTO rpm, which is what I think the OP was asking.
Many posts in the discussion seems to be centered around who peed on the corner of the barn last.
More typically max TORQUE at 540 PTO.
Fuel efficiency would be expressed as fuel volume (or mass) per horse power hour and I don't think we see that very often for Cat 1 and Cat 2 tractors.
It is usually available for small marine diesels and a lot of those are essentially the same as their ag model equivalents.
ROUGHLY 60% of the revs at which they output maximum torque is where they have their highest fuel efficiency.
Yes, tractor/trailer drivers DO INDEED haul in the highest gear and at the lowest revs that will get the job done without lugging.
Whether or not one chooses to believe that the automatic transmission algorithm is based on this, on passenger compartment noise level, or anything else is a choice.
The automatic transmission algorithm precedes EPA regulations by some number of decades, so that theory can be discounted.
I still haven't seen the rationale around the seating of piston rings, but every engine I've ever re-built and seen re-built has had the rings pretty much in the piston grooves when assembled.
PCM recommends some short periods of WOT running under full load after about 20 hours as part of the break-in routine, but warns against prolonged running at WOT even when fully broken in.
