Sorry, I'm using Sandbox+ Mod and there is a command "8 + END - Toggle Slew mode (free camera)". I tried remapping key to example "U" but it also changes command: "U + END - Toggle Slew mode".
http://www.saintsrowmods.com/forum/threads/sandbox-for-saints-row-iv.4651/When you say 'Toggle Slew mode', are you reffering to Toggle Slow mode ?