Why is my phone' screen movements so jittery?

Opening, closing apps seems so jittery the phone used to be smooth when I opened apps. There's always this hesitation when they open and close.

Anyone know what this might be a result of? I close all my apps. I restart the phone. I've reinstalled the operating system snd even restored as s new phone.

None of that has fixed it. Any ideas?

iPhone 3Gs running latest iOS.