You're putting 80-amp pulses through a 3A diode.... and you are wondering why it's burning out? Those diodes are nowhere near sufficient for this purpose.
Its pulse rated for 80A, non-repetitive. This not the same as handling 80A pulses repeatedly...
If the load is around 40A, at 12V, the diode needs to be rated at least 12V (there is no voltage spike because
the diodes there), and able to handle repeated 40A pulses.
Reverse recovery is not relevant for this application, it is forward biased when doing its job.
Something more like a 10A or 20A TO220 diode on a heatsink would be better suited.
If the motor is being PWM'd then the pulses are repeated frequently and thus the power dissipation in the
diode will be significant, hence heatsink. During the time its coducting it will have instantaneous power dissipations of several tens of watts.