Updated

By Larry Fine

NEW YORK (Reuters) - New York Giants co-owner John Mara promised changes on Monday and within hours defensive coordinator Bill Sheridan was the first victim of an 8-8 season that began 5-0 for the 2008 Super Bowl winners.

"Probably as disappointed as I have ever been in my life with this team," Mara, whose family ties to the team date back to its inception in 1925, told reporters at Giants Stadium.

"It is just not acceptable to perform like that. There are 8-8 seasons and there are 8-8 seasons. This one felt a lot more like 2-14 to me."

Mara was particularly irked by a 41-9 mauling by the Carolina Panthers that eliminated New York from playoff contention in their last game at Giants Stadium, which gives way to a new facility across the parking lot after 34 seasons.

"That is not the way we wanted to go out in that building. I felt that loss probably more deeply than any other, particularly the way we were so non-competitive in that game."

The Giants closed the season with a 44-7 humiliation by Minnesota and were outscored 85-16 in their last two games.

"We always used to pride ourselves on being a tough team both physically and mentally. And I didn't see any evidence of that over the second half of the season," Mara said.

The Giants surrendered 427 points, their worst total in 43 seasons, after giving up just 71 points over the first five games in the easier part of their schedule.

"Lack of mental and physical toughness and, quite frankly, a lack of effort over the last two weeks," he said.

"We are going to do what we need to. We are not going to leave any stone unturned."

The Giants had reached the playoffs in four consecutive seasons, which included a Super Bowl victory over New England, and Coughlin and Reese both said they were determined to see the team return to their signature brand of physical play.

"There isn't any question of the physical toughness of these men," Coughlin said. "Its just not demonstrated.

"Execution, production, play well. It's within us. That part of it has to re-emerge."

"We will get that back, but that is not easy. We are not just standing here talking about it. You have to go do it."

Reese said he was annoyed at the lack of cohesion this season.

"If you don't show up on Sunday prepared and play a physical game, and beat yourself with bad penalties and don't play as a team, you are going to lose the game," Reese said.

"This is not our standard. We are 8-8. That is not who we are. We don't want that. We reject that. We are going to make every effort to correct that."

(Editing by Greg Stutchbury)