Although Cincinnati failed to return to the playoffs in 1989, Coslet's unit was again in the top five in the league as they scored the fourth most points and produced the third most total yards in the NFL.
With his successes as an assistant, Coslet found himself highly sought after as a head coach and was hired by the New York Jets for the 1990 season.
The Jets knocked off the Miami Dolphins on the road in the finale, giving Coslet his first playoff berth as a head coach.
In Week 10 against the Denver Broncos, star receiver Al Toon suffered the ninth concussion of his career and was forced to retire after the game.
However, he was given a clear directive by management: if the Jets did not make the playoffs in 1993, Coslet would be fired at the end of the season regardless of the team's record.
The Jets managed to pull off an upset, defeating the Giants 10–6, and carried that momentum to victories in their next four games, capped off by a 6–0 win against the rival Patriots to get to 7–4.
Five days later on January 7, 1994, having refused to give up calling the shots for the offense, Coslet was fired and Pete Carroll was promoted to head coach.
In his first two years as coordinator Coslet's offensive unit hovered around the middle of the league in yards and points scored while the Bengals won a combined 10 games.
After seven games the Bengals finally gave up on disappointing first round draft pick David Klingler and benched him in favor of Jeff Blake, whom the team had signed away from the Jets where Coslet had coached him.
The change paid dividends immediately and Blake nearly beat the two-time defending Super Bowl champion Dallas Cowboys in his first start.
Blake developed a rapport with young wide receivers Carl Pickens and Darnay Scott, who were his two main targets, and Coslet's playcalling used that to the team's advantage.
Although the Bengals once again failed to make the playoffs, Coslet led the team to a 7-2 finish and the offensive unit was back in the NFL's top 10.
Most of that was due to the re-emergence of Boomer Esiason, who the Bengals reacquired in the offseason and who replaced a largely ineffective Blake with five games left in the season.
Esiason won four of those starts, with his only loss coming in a game against the Philadelphia Eagles where he threw four touchdown passes only to be beat on a late field goal.
Coslet elected to give the starting job to veteran Neil O'Donnell, who had just been released from a multimillion-dollar long-term deal he'd signed with the Jets prior to the 1996 season.
After their third consecutive loss, this one a 37–0 blowout against the eventual Super Bowl Champion Baltimore Ravens, Coslet resigned the next day out of frustration and handed control of the team to defensive coordinator Dick LeBeau.
Under Coslet, Emmitt Smith saw his streak of 1,000 yard seasons broken at eleven despite his setting of the NFL's all-time rushing yardage record.