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.