what causes power tailgate to not fully open up so have to push up by hand

Hello, Dave here, contributing to RepairPal and providing expert advice since 2010. I spent some time looking through the workshop manual information for this vehicle and the tailgate - hoping to find a calibration process to change the opening height - but I did not find it. However, a repair shop near you with Toyota experience may be able to evaluate and adjust the opening height. If it's not adjustable, it could be a lift motor or control module that is suspect. They can tell you that too after hands on evaluation. Seek guidance at a local shop. https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.