Do you have access to a scantool to see if your solenoids are kicking in and out?
Also, when you changed the filter...did the new one fit really snug or just so-so?
Losing 4th sounds like it is the start of the death cycle for alot of 4t60Es. After tearing apart my core, I could see why too. But losing 3rd and 2nd at the same time...and after a hard run...I bet you shattered your reaction drum and you're "internally bleeding". Either that, or you plugged your valve body up with crud, which is also possible since you put fresh fluid in not too long ago, and that fluid is washing alot of buildup out of the parts.
No matter what, it'* time to drop the tranny. Or drop the 'buster off at the u-pull-it.
Welcome, downwardly mobile yuppies, to the dawn of the Age of Nefarious.
1993 SSEi - FrankenJinx - dead and gone.
1994 SSE (136K strong) - 180* t-stat,HD alternator, most unequipped SSE on the club, XM radio, Kenwood CD/MP3.
2006 Chevy Malibu Maxx LTZ - Custom 2.25" manifold-back exhaust w/FM-80. Probably the only Maxx with this system.