Only just seen this thread.
To be quite honest, the best mod I did to improve performance and economy...........4.3 diff gears.
With 33s brought everything back to factory. Yes the denco swap improved things, pump and boost is factory - only fuel was increased, and with vehicle weight of close to 4t loaded for a trip, 5th gear overtaking no issues and over $1.30 by the time im at the front of the road train.
If I'm towing, I use a lower gear-higher revs and watch the egt gauge. Always under 500.
Just my observations and opinions.