That is a great departure checklist. I am impressed by your check of hitch and trailer brakes by pulling with the trailer brakes applied.
I do that as part of my departure check routine, but got fooled once by not verifying the trailer electric brake gain setting.
I use trailer brake gain settings between 8.5 and 10 on my rig. Over 3 years of use, and the gain setting has remained at the setting from the previous trailer hitch-up.
A couple of months ago, I departed in light rain on wet roads and did my routine manual trailer brake check. Everything worked fine.
About 30 miles down the road, I encountered a traffic light at the bottom of a downhill grade. It just turned to yellow light. I tried to stop but the brake action caused my tow vehicle to activate the anti-skid braking and my trailer provided minimal stopping power. For reasons I don't know, when I hitched up my rig, the trailer brake gain had set to 3.5. End result is I skidded through the red light.
No damage except for the skid marks in my underwear.
Now I always check my trailer brake gain readout after checking the brake and hitch.
In my case I need 8.0 or higher.