Ever the perfectionist, Sumlin noted things his team could do better again and again after a 73-3 trouncing of Lamar on Saturday night.
"I told them after the game: 'That wasn't our best football. We could play better,'" he said. "We left some things on the table. We had some penalties that were needless. Turnovers."
He believes those are errors that his team won't be able to get away with if the Aggies want to keep pace once they return to Southeastern Conference play on Sept. 27 against Arkansas.
"We didn't win the turnover battle and that can come back to haunt you against other competition," he said. "There are some things that we need to work on."
Texas A&M had four penalties for 45 yards and three turnovers on Saturday night.
Sumlin also had some individual criticism for a pair of true freshmen, Speedy Noil and Myles Garrett, who played big roles in Saturday night's game. Noil, a receiver and returner, had 71 yards receiving, a punt return for 67 yards and a kickoff return for 53 yards to finish with 191 all-purpose yards.
But Sumlin was unhappy with how his punt return ended.
"I got on him a little bit," Sumlin said. "He made some electric plays but I told him: 'We didn't bring you here to fall down at the 4-yard line.' So he was a little upset by that."
Garrett had five tackles, two sacks and two QB hurries. The Lamar offensive line couldn't do much to slow down the 6-foot-5, 255-pound Garrett, who was rated as the top high school defensive end in the nation last season. He has three sacks this season.
But as with Noil, Sumlin pointed out how he could be better.
"I bet he probably missed three or four," Sumlin said when asked about Garrett's sacks. "Those guys aren't going to stand there like in high school. He's not sneaking up on anyone anymore. People are turning protections to him and trying to block him. So it's a learning experience for him."
The blowout allowed Sumlin to play freshman quarterback Kyle Allen. Hill beat out the heralded recruit in camp for the job. He threw for 122 yards with an interception and two touchdowns.
Sumlin likes that the competition between the two has allowed both quarterbacks to get better.
"They both deserve to play and they're comfortable," Sumlin said. "Kenny's probably a little bit more comfortable because he's played more. Kyle got better as the game went on. They congratulated each other ... the competition there is good, but the enthusiasm for each other's success on this team is genuine."
The Aggies host Rice on Saturday before three straight road games against SMU, Arkansas and Mississippi State. Texas A&M is looking forward to another week at home to work on things before going on the road.
Sumlin hopes the experience in a friendly environment will help his young players prepare for tougher competition.
"We're going to need that valuable experience in this league because it's long season," he said. "The more that those guys can play, the more confidence they get and we also get in them."