The old German spec of Gutentight. If you don't know that spec, look it up.
If yours is like mine (Factory FS6), thee should be five bolts to tighten. Two pivot bolts, two "bottom side" bolts, and one "top side" bolt. All of mine had serrated heads. Make sure that all are tight, not just the "top" bolt.
That said, my brackets had a "FAMCO Made in Canada" stamp, so perhaps my setup was specific to Canada-made F150's?
One way you could rule out sloppy fasteners is to tighten it up, then take a paint marker and mark the bolts. When it comes loose, see if the bolts have slid out of the paint marks.
1984 F150: 300 L6, AOD, RWD. EEC IV / TFI, Feedback Carter YFA Carb. Stock everything but radio (for now).