If you suspect a bad bearing, by all means check it out!
If you jack the wheel up and turn it and wiggle it you should be able to tell
pretty quick if it is dragging or rough or loose.
You can change the front wheel bearings with a brass drift and a big hammer.
A plate or a short piece of 2x4 to get the outer race started is helpful and
then you can put the old outer race on top of it to drive it all the way in.
Your gas mileage is SO BAD that it must be something pretty obvious!
I got 33 mpg on one trip in Panama in a 220 at speeds around 80 mph with a big bore
engine and 7001 cam. (300 miles, 9 gallons of gas) First time I ever made the
trip on only one tank of gas! It was late at night and no traffic. Did have OD for an equivalent ratio of about 3.64.

One thing that keeps coming to mind is ignition timing. If it is retarded it will
really put a dent in power, economy and cooling system performance, not to mention
burning up your exhaust system.
--
George Downs, Bartlesville, Heart of the USA!