Not that tuning your engine properly, whether diesel or gasoline, isn’t a good, frugal thing to do.
And don’t forget to inflate your tires properly, too!
As one who reilgiouosly changed oil; set valves, points, plugs, and timing; cleaned/replaced filters; and adjusted the carb(s) every 1,000 miles on my cars way back, I agree.
However... Other than changing oil & filters every 5,000 miles; and, changing (a 3+ hour shop job) spark plugs every 75,000 miles; and making an appointment when the "Check Engine Soon" light comes on, how does one "tune" these computeriszed, electronically injected, shrouded, 'take it out to work on replace it' modern engines?