2008 F-150 Triton. My battery died while driving the other day. AAA tested and confirmed it dead. They towed it to my house where I replaced it. I tested the new battery(was fine) and the alternator. The alternator tested 12.4 in idle. 12.1 under load. I replaced The alternator and the new one tested almost the exact same. Is it possible the new alternator was bad and read the same? Or could there be another issue somewhere? Thank you in advance.

 

The better way to check the alternator is to actually measure the output.
That is measuring the amperage output. When you say under load we have no idea how much you are requiring the alt to put out. Some systems are working fine as long as they maintain a 12 volt reading.
Some charging systems are controlled by the PCM (Powertrain Control Module) which may be set up to maintain an 80% state of charge. You might be looking for a problem that isn't there.
Something you might check and that is all the connections . Especially the output terminal on the alt and the cable/wire from there to either a junction connector or directly to the battery.
Side note, looking at the connections does nothing, need to check them doing voltage drop testing.