Chipping is modifying the actual hardware. You want custom firmware. I don't use slim so I don't know exactly what you need. Go to PSP hack site. You will need to downgrade to 1.0 first and then upgrade to a custom one.
go to forums.qj.net and go to the psp section. what you want is a custom firmware. The most stable custom firmware is 3.90 M33. There are many tutorials on that site.