She just couldn't go 55 MPH

[slick4x4]

Very definitely could have been the head wind
I have ran against the wind & the old 223 just couldn't run fast
Turn around and 1/2 the throttle for the same speed

On the second guess (this has happened to me a couple times)
Truck just didn't have as much power.....
Discovered I didn't have my choke pushed all the way in
Truck ran fine (not sputtering or coughing)
Just out far enough to cut some air supply
Pushed it all the way in .. AND.... Boom ! More power

[unibody madness]

could you have an old and brittle vac advance hose? or maybe its just not seating right?

[bird55]

I know what you mean. Experienced the exact same thing. You might also consider the elevation change. Could be more than you realize, but you would have to check with a GPS or altimeter..

[yellodog]

somewhere you had a brake dragging. that would explain the smell and the lack of power. parking brake possibly?

[bruceandersson]

This is a poser. You were able to downshift and maintain some speed, which would increase your demand for fuel, so it may not be fuel related. My next thought is distributor advance or bad coil. The coil is an easy swap and test. If a coil is marginal, the spark only weakens as the demand on it increases. There is always the old diagnostic charts.

[Toyz]

Wow! Question by question:
Fuel economy would certainly suffer with a dragging brake, which is usually accompanied by a distinctive smell after highway driving.
Coil, maybe; grab an old plug, gap it around .075, plug it into a wire and ground the plug. If it fires across that gap, the coil is probably up to the task.
You can run a compatible Flamethrower coil with the points or a P1; you WILL need to retain your resistor wire.
Quality "performance" wires are usually an asset for general usage, especially with resistor plugs.
The "loafamatic" is certainly not an optimum system; however with the fuel economy you are getting, it seems adequate for your application. You can try different vacuum sources; I am quite certain you will obtain best results with the original routing.
That should give you enough to ponder for the moment, and I am certain other opinions or suggestions may warrant consideration.
Paul

[Toyz]

Just an aside; there are Flamethrower coils which do operate on battery voltage due to the coil's internal resistance. Personally, I would keep the resistance wire, especially with points.
Paul