2004 Toyota Sequoia drivetrain & axles problems

On july 6th at approximately 2:00 in the afternoon my son and I went to pull our boat out of the water with our 2004 toyota sequoia.(we backed the trailer into the water and loaded our boat onto the trailer as we always do. We then secured the boat to the trailer and proceeded to pull the truck and loaded trailer up the hill about 30 feet and parked on the boat launch ramp. I exited the vehicle and left the sequoia in four wheel drive high, in park, with the parking brake on.

2004 toyota sequoia - engine will begin turning over like it is attempting to start without key in the ignition. It turns over like this intermittently every 30-45 seconds until the battery runs completely down. This has happened three times in the past nine months. Dealer states it is ECU computer or starter, but can not determine the exact cause of this. Vehicle has been in for this problem 3 times.