Campbell, 33, was appointed on a temporary basis after the sacking of Dave Penney earlier this month and has since led the relegation-threatened Pirates to two wins and a narrow defeat to high-flying Huddersfield in his three games in charge.
Tunnicliffe, on a season-long loan from Brighton, told the Bristol Evening Post: "Since Cams has taken over, I can't believe the difference in atmosphere amongst the lads. We have a bit of confidence back again now.
"We are playing a lot better than we were doing, so performances are now coming. We haven't been conceding as many goals in the last three games and have kept a couple of clean sheets, and that's what we are going to need.
"If we can keep on doing that then we are always going to get something out of a game."
Source: PA
Source: PA