Those voltage readings are good. So if we use a 220-ohm resistor between the MCU and MOSFET gate, and just drive the pin with digitalWrite() rather than PWM, when the pin is driven high, what are the voltages on either side of the 220-ohm resistor?
You want me to take the motor out of the circuit or leave it in?
Yet when driving a pure resistive load, the voltage looked steady, correct? Does the motor spin at a constant speed or does it act as though it's getting variable voltage?
Interesting ... agree it seems to be pointing to breadboard or wiring or something similar.How many miles on that breadboard? I'm pretty surprised that I don't have more breadboard issues than I do, they're really quite rare, but most of mine are relatively new.