Try downloading a new keyboard app, and see if that still lags. If it doesn't, then it's just the keyboard app that's having a problem. And clear your cashe too...I'll try tomorrow.
On my phone, I use smartkeyboard pro. (Paid ap) But on my tablet I use the stock samsung keyboard.
Smart keyboard is awesome.
I've heard good things about microsofts swiftkey and one called go keyboard. Both are free.