Gas mileage 225 Slant 6

1st up, welcome to FABO @Analogprincess. 2nd, You can see the ballpark You're in above, pretty much typical. 3rd, don't listen to advice from anyone telling You to run "Plus-Silver-etc.", or worse "Gold-Ultimate-etc.". Any more octane than You need makes less power, wastes heat energy into the coolant/exhaust systems, both of which hurts mpgs. I'm not sure what the avg. alcohol content is in Your area, but as noted above, more can hurt....and 87 octane is plenty.
Thanks!