The England international joined Martin O'Neill's side over the summer from Manchester City, but has struggled for form and fitness since his move.
Yet, after scoring in the Mackems' 3-1 defeat to Chelsea at the weekend, the 25-year-old has promised improvement from him and his team-mates.
“I haven't felt a lack of confidence in recent weeks,” Johnson told The Sun. “But it hasn't really been happening for me. It's not been happening for the team, either.
"It's hard to get yourself going when the team's not performing. But we've started to play well and you'll start to see the best of me as well.
|10/3||Adam Johnson is 10/3 to score anytime against Reading with bet365|
"I have to do a lot more, because last season I could stay high up the pitch and didn't have to do much tracking back."
Sunderland face Reading at the Stadium of Light on Tuesday and Johnson admits that it is a must-win game against a team also in the relegation zone.
"The Reading game is massive for us. Everyone knows it's our game in hand and it's important," he said.
"If we play like we did on Saturday, we'll do well. We'll do everything we can to win."