This is because, at 3000 rpm, you are above the "stall" speed of the converter. Stock stall speeds are 2400 to 2600 rpm. Below the stall speed the converter will allow the engine to flash up to the stall rpm. Above it the input and output rpm are linear with a certain percentage of slippage.
Performance converters (some people wrongly call them stall converters, ALL converters have a stall speed) have a higher stall speed to allow the engine to flash up into the powerband rpm.