Have the Bulls peaked? When a team has won 16 of its last 18 games, that’s a question that should be asked delicately. But after another lackluster home victory, it can’t be ignored either. The Bulls emerged as a championship contender with an eye-opening 15-3 stretch after the West Coast trip in February. They beat the Spurs and Heat at home and the Heat and Magic on the road, then won seven games in an eight-game stretch by an average of 21 points, capped by 30-point blowouts of the Kings and Hawks on the road. They looked unbeatable. Since then, the Bulls started showing signs of a team that has hit a mental, if not physical, wall. They’ve struggled to put away the Grizzlies, Bucks, Pistons, Raptors and Suns — borderline playoff contenders at best. They lost decisively to the 76ers at home. The only blowout was against the hapless Timberwolves. The Bulls are 57-20, with the best record in the East heading into tonight’s home game with the Celtics. But even Derrick Rose knows the team is not playing as well as it was. ‘‘A win is a win. But right now we’re not moving in the right direction,’’ Rose said. ‘‘If we’re trying to do something special, playing like this at home, we can’t do that.’’ And the Bulls, who lead the NBA in rebound differential (plus-5.6 per game), were outrebounded for the third time in five games Tuesday night. Read more: http://www.suntimes.com/sports/bask...-bulls-not-moving-in-the-right-direction.html