32g at zero on the screen (or when the light comes on) is pretty close to what i see, also. That's probably a decent assumption if you are going to push it. Keep in mind the long tank means that slopes will greatly affect what the computer says at low levels. Park nose up if you are low and have a hill.

 

 

36 gallon tank.........It is supposed to have 3 gals left when it reads empty....bear in mind your fuel pump relies on some gas in the tank to keep the pump from over heating....Last year when I changed my purge valve (fuel left was pretty accurate @ that 3 gallons) now the guage reads a little more past the full mark than before & also when I fill it expecting to fill with say 32-33 gals I only usually put in around 28-29 gallons ....So a lot changes how the lie-o-meter works with what you have??

 

To me it is about how I trust my indications..:

I like having the DTE display. even though, I don't trust DTE displays 100%.
I find it handy, especially on trips to estimate about where I'm gonna get gas I spend alot of mental energy analyzing the gas buddy app for gas prices , Even though I know, 20 gallons at a nickel a gallon less is only saving me $1 but my brain will ponder it while I'm driving.

In the 3 cars we've owned over the years that had DTE displays they all 3 acted differently..
I took my wife's LHS one day, once I got on the highway I noted DTE read 2..(panic, because it was winter) I got off at the next exit with it reading zero!, filled up, it took 1 gallon more than the advertised capacity (???). but that is an outlier in my normal practice.. When I got home I asked her "Did you know your car was near empty? Yes, I knew you were taking it the next day, and that you don't mind filling it up for me in the winter, so I didn't stop for gas because of how cold it is...(one part of me wanted to be angry, the other part of me realized thru experience, there is NO VICTORY in continuing this conversation.. I chose the latter)
My wife's current car (Subaru) the DTE display only shows 10 mile increments and when you get to <100 miles to empty is goes down fast, fortunately we've have also never run her dry..
As for the gas gauge on the F150, I have at times had it pretty low, and I've never run out of gas so I assume it is accurate enough.. and I do the mental calculation on fill up.... I had 1/4 tank indicated, xx gallons, fill up added XXX gallons, yeah that is close to the advertised capacity...and reset the trip A, and that many miles divided by gallons to fill up is YY MPG, yeah that display is close enough too.