Hi Gavin
This is just my way of hopefully preserving the motor and auto. I do annual trips north and now have 215ks on the D3 with no problems. Auto serviced every 80k. Also many years in the bus game. Besides it gives me something to do to relieve the boredom!
I have a 2008 D3 2.7 and tow a 2900 kg full height van. I don't have EGT but use a Torque pro on an old phone with a Bluetooth OBD adapter to monitor water temp and % load. 
I like to cruise at about 93 kph for fuel economy when no trucks are around and just over 100 kph when they are to keep out of their way.  16 L/100 at 93 and about 20 at 100. Wind makes a big difference, 
My usual mode is sport for takeoff and through towns then on flat open road I lock it in 5th. I find that in auto on a slight downhill it will change into 6th then the next slight rise it does a high torque change back to 5th. I like to stop this happening as it must cause lockup clutch wear. On steeper hills I manually take it back early through the gears to avoid high torque changes. I usually use cruise on the flat country. 
Monitoring the percent load is a bit like driving to an EGT - I had one on my D2. I like to cruise at about 70% load or less. Each gear lower reduces the load at a constant speed. 5th seems to be best for the load we are towing and is what the auto wants to use on average. Unlike the D2 the D3 does not have a 1:1 ratio, 5th and 6th are both overdrives and 4th is under 1:1.
Enjoy the D4 it is much better than the D2 for towing.
The experts will say I am overthinking all this but there you go!! 
Peter
				
			 
			
		 
			
				
			
			
				D4 TDV6 2014, Tow Pro, Traxide, GME, Clearview.
D3 SE 2008 2.7, Traxide, Prodigy P2, Light Force, GME, Sold to my son!
D2 TD5, sold but missed.
			
			
		 
	
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