Amp shut off and came back again.

2" is insufficient room for cooling above most amplifiers! For a space that restricted I would use a fan for cooling. You need a good 10" to a foot above the amp- otherwise even though the heat might not trip the protection, the amp will be running warmer and things like filter capacitors really don't like that- they will have a shorter life.
Adequate cooling is important for any power amplifier.

I didn't realize it was a Class A amp, it really needs more space than that.

Mostly I listen in A/B mode, and the amp just gets warm, not hot.
Class A makes it generate lots of heat.
I'll get another rack or let the amp stands as its own, or maybe use a small fan.