IWCGJQWizard1.Next;
IWCGJQWizard1.Previous;
Dir:= AParams.Values['dir'];
nextIndex:= StrToInt(AParams.Values['newIndex']);
The "newIndex" (or "currentIndex") paramas don't appear to be included in AParams - although "dir" is.
IWCGJQWizard1.JQWizardOptions.OnStepChanging.SendAllArguments := True;