On my 530, I show the 'Grade' data field on one of my screens. I've noticed that there seems to be an incredibly long delay before the Grade registers something. For example, I could be 100yds up a 3.0 grade before it even starts to show. On my old Edge 500it was almost instantaneous.
I've seen about the same lag on the 530 as I had on my old 520. I suspect Garmin is displaying a couple second average. To have it display immediately the data would bounce all over. There has to be some amount of averaging or smoothing to make the display useful. It is a tradeoff between that stability and lag. I'd hope Garmin did some testing to determine what length of average is the best tradeoff.
I seem to remember there being some CIQ data fields that display Grade and give the user the ability to configure the length of time for average. Look around CIQ and see what you find and play with one. You may find a different averaging length you like better.
EDIT: I did a quick look into CIQ. Look at Sensible Grade for example as one that is configurable according to it's description.
