2007 huh? Bet the fluid and filter could use a change. Not a 'flush', a change. Flushing a slush box can do bad things to the valve body. Drop the pan, the fluid and change the filter and pull the plug on the torque converter and drain that as well and then add fluid...
Through the dipstick tube.
Slush boxes have to be the most neglected component in a drive train today and the most expensive to repair / replace and most issues come about from 2 things, first is neglect and second is inadequate cooling of the fluid.