Those hitch vises don't work 100% with extremely heavy loads and big trailers. Although they are better for lighter loads.
Being a once professional welder with building up heavy construction wear parts on earth moving equipment and machinery, I added some hardfacing "buildup" weld metal to my receiver elongated holes as well as the hitch itself.
Granted not everybody has access nor the tools to do this yourself but, one can easily find professional welders to do this relatively simple, effective and inexpensive job. It's the best way to "tighten" things up, without the gimmicks of little "clamp-on" gadgets and such that fail much quicker with HEAVY loads.