The fat agnus from the a500 is only a one meg chip. Wouldn't work even if you pulled the zip ram, and would result (I imagine) in a green screen.
Red screen is a bad ROM. Pull and check the roms for bent pins, replace ROMs and the zips and original 2 meg agnus. See what happens after that.
I'm having the green screen problem with my A3000T also. Waiting for a replacement agnus.
Good luck, the A3000T is an awesome unit.