would it have to do with the adoption of the 960x640 file resolution, to the 1024x768 ipad2 screen resolution?
i'll rephrase: why are the same (large) animated graphics with the same resolution (960x640) fast on an iphone 4 and slaggish on an ipad2?
I am having the exact same issue.
I have created a game and tested it on the iPhone 3GS using GPU rendering and it runs perfectly.
I have tried to port the exact same game to the iPad 2 and it runs horrifically slow.
I'm currently trying to figure out the issue but havn't found any answers so far.
My only guess is that Adobe AIR has VERY POOR performance on the iPad 2.
If you can figure out any way of fixing this, please post your fix.
Status update on my situation: SUCCESS!
I've been able to solve the lag issue by updating my Adobe AIR.
Flash CS5.5 comes built in with AIR 2.6 and has horrible performance compared to the latest version of AIR 3.1
You can find a tutorial how to update your Adobe AIR (since you cannot update the version of AIR preinstalled in your Flash CS5.5, you need to do it manually)
You can figure it out here: http://kb2.adobe.com/cps/908/cpsid_90810.html (its the exact same for AIR 3.1)
Make sure to follow the instructions properly.
Additional (older guides) can be found here: http://blog.prevail.co.nz/2011/06/21/overlaying-air2-7-in-flash-cs5/
Good luck and hopefuly you'll fix your issue.