Mosfet IRF7457PbF voltage drop too high
You are using the MOSFET as a voltage follower. In other words you have drain connected to 12V and the source connected to the load. To switch on the device, the gate voltage needs to be a few volts higher than the source and your results demonstrate that i.e. Vin = 9.4 volts and Vout (source) = 7.55 volts i.e you have a volt drop of 1.85 volts trying to turn on the device.

Of course this isn't enough - if you read the data sheet, to turn the device on "properly" you need at least 2.7 volts (figure 1 page 3 of data sheet) and, to turn it on so that it produces 12 volts out means applying 14.7 volts to the gate.

I suspect you should be using a P channel device wired so that it can turn on hard with a gate voltage taken down to 0V: -