as of right now, there is no way to downgrade, and i haven't heard of any development on it.. i would just recommend buying gta, because homebrew on the 2.6 is coming a lot quicker than the downgrader! good luck!
aperrently i almost found a downgrader. i tried accesing the innernet at my school and it screws my psp up and the same blue screen that comes up when you use a downgrader came up...dose that mean im realy close?