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Pat Sullivan, Associated Press
Texas A&M wide receiver Jeff Fuller, left, loses the ball under pressure from Missouri defensive back E.J. Gaines for an incomplete pass during the second half of an NCAA college football game Saturday, Oct. 29, 2011, in College Station, Texas. Missouri won in overtime 38-31.

COLLEGE STATION, Texas — Texas A&M planned to contend for the national championship when the season began and still had hopes of grabbing the Big 12 conference crown after two early defeats.

An overtime loss to unranked Missouri last weekend makes that goal far less likely. The Aggies are grasping for ways to get back on track and it won't be easy this week on the road against No. 7 Oklahoma.

Texas A&M has lost six straight games at Oklahoma and is 13-2 overall there.

"We can't wallow in our despair, we have to move forward," Texas A&M coach Mike Sherman said. "As disappointing as it was to lose the ballgame and as frustrating as it is, the true measure of a team is your ability to bounce back and rise above it all."

Texas A&M entered the season ranked in the top 10, but early losses to No. 3 Oklahoma State and eighth-ranked Arkansas knocked the team out of the national championship hunt.

The Aggies have led by double digits at halftime in each of their losses this season. Some have wondered if the Aggies get into the 'here we go again' mindset when things start going wrong after halftime and can't stop the snowball effect.

"It's certainly something I've considered, but it's not an excuse for us not being able to handle the complexity of the game and how it unfolded," Sherman said. "We have to be better at delivering the knockout punch and we haven't done that in those three games."

A&M's offense is ranked seventh in the nation and is averaging almost 520 yards a game. Quarterback Ryan Tannehill said it's difficult to realize the Aggies were in a position to win every game this season.

"It's frustrating, but at the same time it's not how it worked out," he said. "You have to be truthful with yourself and move forward. Do I feel like we should have won those games? Yes. But we didn't. We have to pick up the pieces (and) move forward this week."

Texas A&M managed just three points after halftime in the 38-31 loss to Missouri. The Aggies struggled with dropped passes, missed blocks, penalties and an inability to convert third downs in the second half. Defensive coordinator Tim DeRuyter also said his team had its most missed tackles of the season last Saturday.

"We are still having too many critical errors that we can't have," he said. "Our guys were starting to get some confidence. But we're not responding to adversity the way we need to right now."

Sherman is challenging his veterans to step up as they face two tough road games, with a trip to No. 17 Kansas State coming up next week.

"I think we can always be better, particularly in times like this," Sherman said. "It's easy to be a leader when you're winning games, it's tougher when you aren't."

The Aggies beat Oklahoma 33-19 at home last season, but know they'll have to be good for four quarters on Saturday for any chance to compete with the Sooners this year. Texas A&M hasn't won two in a row over Oklahoma since winning four straight meetings ending in 1998.

"Consistency defines greatness in my mind," Sherman said. "You have to be consistently great or good to be that. We certainly are lacking that consistency."