I'm pretty sure both Canada and US get the same physical 26 and 33 gallon tank. There is just some mistakes on the website listing what the correct size is, based on conversion errors.
He's saying his truck reports his MPG in UK gallons, which means it will always read as far better MPG than it would when reading with US gallons. The UK gallon is bigger, you can drive more miles per gallon when your gallon is bigger.
That's also (partly) why it seems European cars get better MPG than American cars. We're using different gallons. They do have tiny little lawn mower engines though, 1.x liters are not at all uncommon there.
They don't get the same tank. There is no conversion.
I'm not sure what he means UK gallons. If he is in Canada they don't use US gallons. If\when OP responds with more information we can any idea what he is actually trying to say any maybe help him change with Alfaobd.
I wouldn't call .3 MPG difference "dead on" and every truck will be different. Unless zim doing long highway drives, mine is almost always .5-1mpg different when calculating vs displayed. I've seen as much as 1.5 MPG difference. And the EVIC display is always better than actual.
We are talking about a 1-2% difference in what my screen shows vs my actual. That is dead on to me.
I don't do much city driving and when I do I don't sit at stop lights or traffic so i'm not wasting gas hanging around.
The screen always shows i'm getting .3 mpg WORSE then what I actually get.
I have a 33 gallon tank, and I only get gas if I am under 1/8th of a tank. Generally between 27-30 gallons each time I fill so a decent sample size.
I also reset my trip b each time to use for each tank of gas.
In prior cars\trucks my computer always shows much better numbers then the auctual, sometimes as big a difference as 3MPG on a full tank but generally 1-2mpg difference, screen showing better then actual.
This truck shows the most accurate so far, but obviously don't relay on it...