A couple months and 20 pounds later, Johnson is embracing a move that could extend the former seventh-round pick's NFL career indefinitely.
To be honest, the decision came as a bit of relief for Johnson. He spent last season meeting and practicing with the tight ends all week only to be thrown into the backfield as a lead blocker in goal line situations with little preparation.
Now Johnson - who will keep the No. 85 - sits in meetings trying to absorb as much of new offensive coordinator Todd Haley's playbook as he can while getting a feel for what his role will look like when the season starts in September.
"It's actually a little bit easier," Johnson said. "That's all I've got to learn now is fullback. At first I had to know both tight end positions and fullback. Now I just focus on fullback and just create my better habits on that and become the best at it."
The position, once a mainstay, has been phased out by most teams in favor of three-receiver sets even in Pittsburgh. The spot has been vacant since Dan Kreider left the team following the 2007 season as former offensive coordinator Bruce Arians opted for a more pass-heavy attack.
While Haley still plans to let quarterback Ben Roethlisberger do his thing, he also wants to give Pittsburgh's running game a physical presence it has lacked at times since Jerome Bettis' retirement following the 2005 season.
Haley utilized a fullback expertly while head coach Kansas City from 2009-11. Tim Castille helped pave the way for the Chiefs to lead the NFL in rushing while winning an unlikely AFC West title in 2010. The team then signed Le'Ron McClain last season, with the former All-Pro keeping Kansas City productive despite a rash of injuries.
Johnson will try to do the same for a backfield missing Rashard Mendenhall, who remains out indefinitely as he comes back from a torn ACL in his right knee.
Isaac Redman will get the first crack at replacing Mendenhall. He ran for an eye-opening 121 yards in a Wild Card playoff loss to Denver, some of the yards coming with Johnson smashing into linebackers.
Hey, it beats Johnson's old job, when he would try to ward off 300-pound defensive linemen. It's more of a fair fight at fullback, and though he's trimmed down, Johnson allows he's "still pretty big."
And not too tall. At 6-foot-2, Johnson is short enough where leverage won't be an issue. Part of his job description is to pick a target in front of him and get low. Not a problem for a player Miller considers one of the better athletes on the team.
Johnson hopes his willingness to take on the position and his soft hands will still make him a threat when he's not sticking his helmet into tight places. He caught 12 passes for 91 yards and a touchdown a year ago.
Haley's system gives his backs chances to catch the ball. McClain hauled in 14 passes for Kansas City last year and Castille grabbed 10 in 2010.
Those numbers are fine by Johnson, who doesn't expect to be handed the ball by Roethlisberger. Johnson's last carry as a running back came during Pop Warner.
"I'm OK if I get a couple of passes in the flat," he said.
Anything to stay on the team. Johnson knew his role as the team's No. 2 tight end behind Miller was in jeopardy after the rise of rookie Weslye Saunders last season and the signing of veteran Leonard Pope.
He accepted the move with open arms, knowing being more versatile can only help him stick around.
Besides, being a fullback may be the quickest way to the Pro Bowl. Though the position is increasingly rare, the best at it still earn a trip to Hawaii at the end of the season.
"I hope so," he said with a laugh.