How to get a fresh start

[s4boost]

My jailbroken iPhone 4 on 4.2.1 has been lagging. I've manually deleted some launch demons and I do have more available ram now but it didn't get rid of the slow folder opening or the home button lag.

Is there anything else I can do to fix this?

I was thinking about doing a clean 4.2.1 install and then rejailbreaking the phone, can I do that or will apple force me to upgrade to 4.3? Does anyone have more information on the correct procedure for a clean install of 4.2.1 if it is possible?

Thank you

[s4boost]

Btw, as far as I know I do have the 4.2.1 shsh saved in cydia

[Wessy]

I had same problem and tried what you have suggested. I could not get 4.2.1 to install. Had to downgrade to 4.1 and that worked then jailbroke. Phone is more responsive and battery life is better.
Wessy