My /6 is a gas pig when it's cold outside. Why?

First, no matter how bad the mileage, I doubt you would notice the tank level drop in a few miles. More likely, the gage reading is changing as it heats up. Higher temp = more resistance = lower indicated level.

One thing often over-looked in choke operation is the importance of the vacuum "choke pull-off" or "unloader". Insure yours doesn't have a torn diaphragm. Remove the hose, push in the stem, cover w/ finger, see if it stays in (after initial outward movement), or test w/ a vacuum pump. If it comes out all the way, the diaphragm is torn (common) and it won't do its job. Which is to pop open the choke slightly the second the engine fires. You need the choke fully closed while cranking. You should also see that happen as you start a cold engine. Without it, you will never adjust the choke to work well. I fooled w/ that on my 69 Dart slant for years in younger days, not understanding it.

You didn't tell us what carb you have. I think 1973's had more complicated cold-start controls, though 1974 was even more (big vacuum amplifier, ...).