Trim rams hard to retract, please diagnose

[G3yamaha]

I have a 2004 Yamaha ox66 200 with a trim issue that I need help diagnosing. The motor tilts up and down perfectly, and trims up perfectly. The problem is the motor trims down very slowly, and is very strained. It seems like the trim rams are not releasing pressure appropriately. Any thoughts on why the trim rams are having trouble retracting? Visually, they are in excellent condition (no corrosion, etc.). Most people seem to have trouble going up, not down.

Things I have done:
1. Bleed the system many times, checked fluid, etc.

2. With the motor manually locked in the up position, the trim rams are retracting on there own when I engage the button, but sound very strained and are slow.