If it gets hot that fast, and shuts down before it kills itself <in like 10-30 seconds> gotta be an ohmage problem with the sub. Maybe the amp isn't 1 or 2 ohm stable, when your other one was. Could be an intermittent VC short in the sub, which is what bombed your old amp, and might eat this one, too.
What amp and what subs do you have? Ported or sealed boxes?