If you want massive fuel consumption and high engine RPM turn the OD off and the transmission won't shift higher than 4th. Why would anyone do this?

I tow my 5000 pound camper with OD on and she runs at 1800 rpm in 6th gear. Sometimes she'll down shift to 5th and less down to 4th. No point in running 4th gear all the time if you only need it 10% of the time.

HD Towing package gets you about 9000 pounds max capacity. 3000 pounds won't be much of a bother at all, our 5000 pounds barely is. I've monitored transmission and engine coolant temperatures and only trans temp shows any rise from normal driving and that by 10° or 15° at most. Engine coolant remains below 200°.

-- Chuck