I'll respectfully beg to differ. I've filled up with 5.3gal numerous times and 5.4gal a couple times using the same station / same pump for those tanks. Once I did get a bit of a stumble when on the brakes.

I refill to the lower rim on the tank.
I have wondered if 5.5gal is usable fuel or includes the trapped/unusable amount and what that amount is. I agree that there is some unusable amount down in the cheeks of the tank.
I've never had the opportunity to measure the real capacity after a fuel filter change, but it would be interesting to know.
Fuel and oil pumps are a bit of a marvel to me. Holding 45psi constantly running for thousands of miles. The oil pump doubles that pressure. Yes, both fluids are lubricants, but still.
Have a good one.