TCU will have to dominate Southern Miss in a serious way to finish in the top 6. TCU is dropping because the big guys are playing big teams and winning. Their strength of schedule is overpowering their 2 losses.
TCU has to make a statement to voters in order to be ranked higher in the human polls.
BTW, the reason TCU is ranked so high in the computer polls is that margin of victory is dissallowed in the BCS. Sagarin publishes two polls, one for the BCS, and one with margin of victory.
Here is Sagarins poll on USA Today http://www.usatoday.com/sports/sagarin/fbt03.htm
TCU is ranked 34th in his "non-adjusted" poll. Using his ELO-CHESS methodology (no margin of victory) TCU is ranked 8th.
The discrepancy isn't limited to TCU. Sagarin has Ohio ST ranked 13 using MOV, they are ranked 3rd using Elo-Chess. For all of Craig Krenzel's pregnant doging about TCU being ranked to highly due to margin of victory, he fails to point out his Buckeyes are also in the same boat. Granted, the Buckeyes have a much tougher schedule than TCU, if they finish with one loss, they do deserve a Sugar Bowl bid.