Looking at some of the why's, where's and how's of  a heavy truck burning its fuel...  a balancing act 

The  Physics of  truck fuel consumption

 Truck worlds core view of the Physics

Issues and nuances 

 Solution Source

Parasitic Losses

Internal frictions

Understanding the balance between the engine, transmission and drive train - along with its' greases & fluids

Spec, spec, spec & maintenance

 Momentum & Inertia 

speed, speed change; up, down, flat

Avoiding accelerating twice when once will do 

Driver, driver, driver as the momentum manager...?

Overcoming the friction of Air Resistance

High Drag, Low Drags

 Shaping a rolling box into a space ship

Mfg, model + spec & balance

Speed & Air

Physics Cubed

Dispatch + driver

Road Frictions - never a wind at your back

Treads, alignments, pressures & surfaces

Often ignored... as dollars turn to dust

Specs + Ownership control

Parked & in bed

From where comes comfortable temperatures?

Engine, APU’s, and other comfort strategies 

 research, tradeoffs - driver implementation

 Excess Miles

 dispatch error, driver error, road conditions

 communications - GPS, Satellite, Cell Phone, PCD

 research tradeoffs & capitalize on internet based solutions

 Impact of weight

 more mass, more work required

 markets served

 ownership or controls 

The above are fuel cost talking points - hundreds of pages could easily be expanded and written on the topics introduced in most of the boxes, the tradeoffs - the costs - the benefits... the balances.  

You may note from the above, that when a truck is moving, other than excess miles off route, the driver only has control of one thing that has an effect on fuel economy.  

There are; no one shoe fits all, no no-tradeoff answers, and few absolutes to getting low average fuel costs relative to your peers... but there are approaches that work, balancing the spec's to minimize tradeoffs and reduce risk.