I've seen that one before. Transmission Throttle Valve Actuator (TTVA). I searched the forums a while back when my dad's '06 had that code pop up but I didn't find any info here, surprisingly.
Spoke with the shop that rebuilt the transmission and they hooked up their scan tool and checked the actuator and found it to be operating normally. At the time, we had other ECM issues to deal with. Specifically, they checked the response of the throttle position sensor from 0-100% and starting position angle in degress, which, on my dad's truck happened to show 3degs.