U cant downgrade a Slim............yet. Dax is working on that. So check back in........i dont a week or so. At the most a month and then i bet there will be a Pandora battery for slim.
and right now the only 2 slim CFWs are 3.60M33 and 3.71 M33. You have to have an original 3.60 first on the slim tho.
u may not be able to downgrade the slim but you can install custom firmware on it and that would be 3.60M33 you can find the tut here but the only unfortunate thing for you is you need another "fat" psp that is already homebrew enabled so i would try a friend or something
My Psp Life> 2.6>2.71>2.80>3.03>1.5YES!>3.03OE-C>bricked!>1.5>3.03OE-B>
bricked!>1.5>3.03OE-C>1.5>3.03OE-C>3.40oe-a>3.52M33-4