LED not achieving max current
According to the chart on page 17 of the datasheet, the terminal voltage of a nominal-9V LED rises to between 10.25 and 10.5 V (depending on temperature) at 1 A. You need to size your resistor accordingly.

But it would be far better to use an active current regulator to feed this kind of LED. Then, the current wouldn't depend on temperature. Or on your actual source voltage, for that matter.