Thanks for the suggestions regarding Teflon tape; I'll give it a try.
No matter how I tightened the new knob (from Steeda) sooner or later it loosened.
If its an aftermarket shifter, there should be a counter nut that you snug up against the shift know and it should keep it there snug and secure.
2011 Mustang GT M6 3.31s
Matt HONEYCUTT Tune, Lethal Off-Road X, GT500 axlebacks, J&M LCAs, UPR UCA, Whiteline LCA relocation brackets, Eibach Pro-Kit Springs, Koni STR.T shocks/struts, GT500 strut mounts, SR Strut Tower Brace
Best 1/4 E/T (05/18/14 MIR - no tune, X-pipe, or UCA): 12.920 @ 109.40 mph (2.059 60ft)