PITTSBURGH — James Harrison expected his body to be sore while working his way back into football shape following a nine-month break.

Turns out, the five-time Pro Bowl linebacker’s in better shape than he thought. He played 29 snaps in the Pittsburgh Steelers’ stunning 27-24 loss to Tampa Bay last Sunday, far more than he anticipated when the Steelers signed him off the couch a week ago.

The harder transition proved to be mental. He failed to register a single tackle and was a non-factor in the pass rush in part to being out of position at times.

“I had a few MEs (mental errors) out there,” Harrison said.

The 2008 NFL Defensive Player of the Year isn’t alone. Despite revamping a defense in the offseason to focus on speed and youth, the Steelers are still struggling to create the splash plays that came with such ease during their three Super Bowl appearances between the 2005 and 2010 seasons.

A fitful September mercifully in the rearview mirror, Pittsburgh (2-2) heads to Jacksonville (0-4) on Sunday searching for consistency and more than a little bit of snarl. The Steelers have produced seven sacks through four games — 18th in the league — and forced only three turnovers, one on a fumbled punt.

Pittsburgh expected growing pains while working in a handful of new faces. Four uneven games into the season, those pains show no sign of going away.

And it’s not just the kids making the miscues. Outside linebacker Jason Worilds, in a contract year that will likely determine the course of the rest of his career, has one sack. Arthur Moats — thrust into a starting role when Jarvis Jones was lost for at least eight weeks with a wrist injury — couldn’t find his way to Tampa Bay’s Mike Glennon on Sunday. Neither could Harrison, who could only watch as Glennon stepped up in the pocket time after time during a fourth quarter rally.

For Pittsburgh’s plan to reach the NFL elite again to work, opposing quarterbacks need to get uncomfortable.

“I’d like more from that (linebacker) group and I think that group is definitely capable of giving us more,” coach Mike Tomlin said. “But also I think some game circumstances will help us in that regard.”

Playing with a sizable lead would help. Pittsburgh showed flashes in the second half of a 37-19 win over Carolina on Sept. 21. The Steelers held Panthers quarterback Cam Newton in check and didn’t give him time to get set, the byproduct of knowing Carolina had to throw the ball to get back in the game.

Jones changed the momentum for good with a third quarter strip sack.