This example demonstrates how to retrieve the unique ID number for a Slide object and then use this number to return that Slide object from the Slides collection.
Set gslides = ActivePresentation.Slides
'Get slide ID
graphSlideID = gslides.Add(2, ppLayoutChart).SlideID
gslides.FindBySlideID(graphSlideID) _
.SlideShowTransition.EntryEffect = _
ppEffectCoverLeft 'Use ID to return specific slide