If the Timbrens mount inboard of your leaf springs on your '18 F350, it's possible the Timbrens are aggravating your sway situation. If they are mounted inboard, may want to consider removing the Timbrens and installing a set of upper and lower Torklift Stableloads. The Stableloads work/operate in the most outboard position possible (on the leaf springs) so they're able to provide both sag and sway reduction.
FWIW, Truck Camper Magazine reviewed the larger diameter RM sway bar and reported a significant decrease in sway.
