Some of the more basic, or older EFI systems do not tune for altitude on the fly. They sample the barometric pressure at startup only and that is it because they read it from the same map sensor it uses to determine engine load and the only time it sees atmospheric pressure is before the engine cranks.
They take the initial reading (like my TEC II does) then use the O2 sensor to correct the air/fuel ratio as you drive through altitude changes. That's more than sufficient in the vast majority of situations. After all, altitude means less oxygen. That shows up as a rich condition so the computer backs off the fuel as frequently as it samples.
It's pretty rare to find a carb tuner who can make several changes each second.
