91 Celica Gt Gas Mileage

[Old Red Celica]

That does seem a bit low, but I guess you're basing that on US Gallons.

A US Gallon is 3.8 Litres and the UK one is 4.5 litres.

In the UK I'd expect to see 28-30 MPG (UK) which equates to about 25 MPG (US).

When on a steady run, there would be no reason why you should not get 30MPG (US)

Are you driving at a sensible speed? Air con on? Windows shut? Sunroof (moonroof) shut?

All of these factors will hit fuel consumption.