[touch-this-pro]

ok, I am going to also give my 2 cents,

I had the same problem with many contacts and texts when I upgraded to sprint 6.5 rom.

All I did is to switch from threated to Classic and the viola, no more lag.

I believe is that in the treaded mode, all the texts form the same person load when u view a message and when they are thousands, it bogs down the phone.

I switched back to threated just to verify and surely enough the problem came back on.
Now I am on classic messages at all times (you loose the coolness factor with the treaded messages thought).

hope it works