Gas Gauge Stuck?

[tomfg]

Fill up gas tank all the way today on the 64 for the first time
since I've had it on the road. Went on a 90 mile shake-down
cruise, and the gas gauge never dropped off of full.
I know it actually burned gas, as I filled it back up
when I got home to calculated the mileage, and had
to add 8.45 gallons.
The gauge did seemed to operate okay between
empty and 1/2 tank before today when I filled it all
the way.
Is it possible the float is stuck, or that something
else happened? I did have the float out when
restoring the truck to inspect it, and don't remember
any mechanical issues with it.

Also, the gas milage came out to 10.76 mpg.
Does this sound about normal, having
a 350, with a 2 barrel, sm420 4spd, and
3.73 gears in the rear? The tach is showing
about 2600 rpms at 55 mph.

Thanks for any input.