PITTSBURGH -- Dan McCullers is not just a defensive tackle. He's a walking baobab tree with a reach as wide as an IMAX movie screen.

The mere presence of this mammoth, 6-foot-7, 352-pound man causes a double take, even when you see him every day.

That's why McCullers' production -- 10 tackles in 21 career games -- is a bit curious, prompting defensive end Cam Heyward to stress at organized team activities that McCullers must "put it together" and "play humongous" in his third season. The Pittsburgh Steelers obviously expect the same after letting starting nose tackle Steve McLendon walk this offseason.

But there's been something missing with McCullers on the field. According to Thomas Simms, McCullers' agent, McCullers made a few changes this offseason that should help.

First, McCullers got offseason shoulder surgery, a minor scope to clean out cartilage and correct an injury suffered during his career at the University of Tennessee. "After three to four [defensive] series, it would start to hurt and he couldn't get off blocks," Simms said.

That helps explain his struggles in 2015, when in training camp McCullers would toss an opposing lineman like a Frisbee on one play, then disappear for the next several.

McCullers also got contact lenses. He was squinting a lot, and Simms started to wonder whether McCullers had issues seeing the board in team meetings. The two talked about it, and McCullers got examined.

In addition, after playing closer to 400 pounds at Tennessee, McCullers has kept his weight around 350-plus pounds.

"This year, I think they will see a different Dan," Simms said.

After Wednesday's practice, McCullers acknowledged hand usage and fundamentals have been an issue, but when he cleans that up, which he hopes to do soon, watch out.

While other Steelers defenders from the 2014 draft, such as linebacker Ryan Shazier and defensive tackle Stephon Tuitt, are taking off, McCullers understands it's time to join that group.

"I can be a dominant player,” McCullers said. "I just have to keep working. That's the big thing, keep working on my technique and fundamentals. I can be dominant. I know I can.”

The Steelers drafted defensive tackle Javon Hargrave in the third round, but he's a quicker, squattier player. He can play inside and also has pass-rushing skills. McCullers is a true run-stopping nose tackle, which the Steelers only use about a third of the time, but it's a key function for a team that takes pride in its play against the run.

The Steelers offered McLendon a multiyear deal, but the New York Jets offered three years and more money, so Pittsburgh decided to roll with Big Dan and a draft pick in the middle. They also signed Ricardo Mathews as a rotational guy.

The Steelers' offseason moves at tackle -- or lack thereof -- got McCullers' attention.

"When [McLendon] left, I knew it was my time to step up and be the starter," McCullers said.