When I got my '77 Aspen (318 auto) it didn't run all that well. Went through the usual maintenance, replacing all fluids and consumables. New spark plugs, ignition module, cables and even a brand new Firecore distributor. Set it up with a timing light at 10* BTDC and had a pro double check on my installation.
Decided the old Carter BBD had seen better days and replaced it with a reman unit to keep things simple. Well, I now get around 5 mpg in town. Terrible for a daily driver!

First place to look would be the carb and it is running slightly rich but when setting it up I used both a Colortune spark plug and my vacuum gauge and it seemed to run well. Leaning it out certainly didn't help, car would immediately start running rough and eventually die. Vacuum was a tad low at 16 inHg but remained stable (worn rings?)

I plan to eliminate most of the EGR stuff as it may be causing a vacuum leak and it's not required anyway but I'm a bit lost where all that fuel might be going. It's not leaking from the tank, that's for sure!