if you updated the console then the only way to downgrade back to 3.55 is with a e3 or a progskeet. inside a playstation update file there are several smaller .pkg package files that update different regions of the ps3, only dev_flash is stored on the hard drive and the more important core_os_package.pkg is flashed onto the nor chip so we clip the e3 device onto this chip and make a backup because it stores some very important console data then basically we reprogram the consoles chip with data from the 3.55 package file and then you can reinstall 3.55
The e3 has all that you need. The nor flasher still needs a way to connect the hard drive to the ps3. So one could buy a sata station and that would do. You have to remember that when you are dealing with the e3 there is a clip system in it and if that is not sitting on there right it will make a bad dump and if you write with a bad dump then you are not going to get your ps3 back from that.
if you do this make sure that you post your dump up and have someone check it and make sure that it is right before you do anything else. thanks and if you would like we have some people that will do the downgrade for you for a fee and you don't have to worry about it. thanks