Do you use a good heat sink? Did you check the gate voltage to be in line with specifications?
Driving a "beefy"MOSFET means that gate voltage must open its channel. If open, the channel resistance drops to ~10 milliOhms, this is why MOSFETs are preferred as current switches. If not open properly, the channel keeps a higher resistane and its dissipation makes MOSFET hot.
Do you use a protective diode across the channel? A brushed DC motor can kill the MOSFET due to voltage spikes.