Any suggestions?

[Govern]

I know it's been touch on a lot but I'm getting stumped.. Having poop fuel economy 8mpg tops. That's w a very light foot. This is what I have done to improve the issue but it still occurs

1 new msd dis
2 new wires
3 plugs gapped at 40
4 sealed all vac leaks
5 new edelbrock 600 tuned w vac gauge
6 new air filter
7 initial timming is at 12 advanced
8 vacume gauge reads 20-21hg at idle which I think is really great for a old 350
9 bfg tires inflated to 30 psi 35"
10 456 gears
11 700r4 trans

Reading on here people w similar combos are reporting closer to 12-14 mph and tips? Am I missing something