MY phone 1013 shows up when restoring, has 4.2.1,, 05.15.04 installed. If successful restoring, can I revert back to 3.1.2 Ipsw? Is 421 a power hog?

I restored to 3.1.2 but "no service" for this phone with a valid sim card for this proper carrier.

Had to use recboot.

Now says restore needed. Can someone please help?

05.15,04 boot 6.2 Model MB629