[Jake101]

I only drove semi for 32 years, but the best advice I ever got about hitching up was to back under the trailer, with the trailer just under the height of the 5th wheel. After backing under the trailer, chenk that the jaws are closed around the king pin, and not high hitched. Then do your pull test. In 32 year with semi I never high hitched, knock on wood, and never had a trailer unhook because the jaws were not closed. It is so easy to miss if you don't get in the habit of doing things in order. Good luck in the future.