Factory convertors usually stall around 1400 RPM. Rated stall is the RPM the convertor will let the engine "flash" to in a full throttle start.

IE, a 3000 stall convertor from idle to the floorboards will let the engine jump to 3000 RPM for a harder launch.

HOWEVER, not all engines effect a given convertor the same.

The more torque the engine makes the higher the stall point.

So, a 3000 convertor in a mild small block powered car might stall at 2700, and the same convertor in a "healthy" big block powered car might stall at 3100 plus.

For a mild street application shoot for about 2200 stall, you'll notice a BIG difference.