slow-moving loop

Hey all.
I have a really slow-moving loop here. not sure why

72 small pics on the screen with background images behind them.

I made them invisible to swap the images, then re-visible

For t = 1 To 72
picBackground(t).Visible = False
imgForeground(t).Visible = False
Next

'change out pics
For t = 1 To 72
picBackground(t).Visible = True
imgForeground(t).Visible = True
Next

I made them all invisible and revisible to avoid the "sweep" effect as the pics change, but they are going invisible one by one, not instantly.
I have a top-notch CPU/MOBO/RAM/Video Card, so I don't think that's it
I thought the pics might be too large,and since some were pretty large, I thumbnailed all the pics so that they are now all around 3kb JPG
No difference
I'm wondering if it is going past the Next and trying to start loading the new images

Any thoughts?
Also, I remember in VB6 it was easy to lock the screen while making big changes and then unlock it, and that avoided the sweep effect.
Haven't seen it in .Net

Thanks all