Of all the changes I made, the single biggest difference came from driving slower.
Yes, it lacks overdrive so highway RPMs are high, but is there really ever any need to go above 60mph?
So many good reasons to drive slow: your risk of death drops dramatically, your fuel use goes down (saving both money, clean air, and our country's security), you have less stress - all with less cost in time than you probably think.
See:
Neapolitan: Slow down. My philosophy for life also applies to the road.
for my complete essay on driving slower.
As for the heat, our truck has a built in block heater (at least, mine does).
Also, replace stock fan with thermostat controlled electric, and add a grill block.
See
Vehicle efficiency upgrades: 31 MPG (so far) in 2.5ton commercial truck for more