It's unclear as to whether the guy in those vids is claiming to run that truck TOTALLY on HHO - or simply supplementing the diesel fuel - I suspect that he is only supplementing the diesel - AND, if he is attempting to show with ONLY the computer display what his "gains" are, that is entirely misleading - ONLY longer test runs, with reasonably measured mileage and fuel volume are a "test" - computer readouts are NORORIOUSLY inaccurate in situations like this - Hell, I often show over 40 MPG at 60 MPH on flat ground - but usually do a best of a bit over 22 MPG in actual MPG.
MPG computers LIE - and are easily compromised in actual delivered MPG...
I want to believe this stuff as much as the next guy - but those vids are worthless by themselves!