[mr48chev]

You answered your own question when you said that when the truck warms up to 180 the heater actually kicks out heat.
It's 25F outside right now and I just made a 70 mile run with a 180 thermostat and it barely warms up enough to make the cab comfortable.
I have to ask, how can you tell that you loose 8-10 hp when the truck runs at 180 or a bit higher or is it all in your head?
Back when everyone ran hotwater Chev sixes or flatheads anything over about 180 was pretty warm but on modern engines 180 is just getting up to good operating temp for most street engines and the old ideas really don't stand up.

Or do like guys did for 50 years or more and put a bit hotter thermostat in for winter and a cooler one for summer. That used to be the normal thing to do in the 50's.