iPhone 3g os4 too slow to work – downgrading

As many other uses who have iPhone 3G and updated to OS4 noticed that their phone after some time is almost unusable or this. I have installed SBssetings which shows me free RAM and i noticed when RAM is lower 10MB phone doesn’t respond and can’t work properly.  (Some memory leak ? not sure)

So I have decided to downgrade to 3.1.3  and it is not as easy as you would thought.

I want my phone to be jailbreaken so you have 2 options:

1. find already customized firmware (search for customized restore firmware)

2. customize firmware yourself 🙂

Everything was ok, except that I got error 1600.

I have solved this issue by setting iPhone NOT in DFU mode but in RECOVERY mode.

There is another application for this issue “IREB” or this but it didn’t work for me (I think it works for 3.1.3 but not in os4).